diff --git a/bench/src/main/scala/Benchmarks.scala b/bench/src/main/scala/Benchmarks.scala
index ec152b5336fa..60206de54f9a 100644
--- a/bench/src/main/scala/Benchmarks.scala
+++ b/bench/src/main/scala/Benchmarks.scala
@@ -30,8 +30,11 @@ object Bench {
     val iterations = if (intArgs.length > 1) intArgs(1).toInt else 20
     val forks = if (intArgs.length > 2) intArgs(2).toInt else 1
 
+
+    import File.{ separator => sep }
+
     val args2 = args1.map { arg =>
-      if ((arg.endsWith(".scala") || arg.endsWith(".java")) && arg.head != '/') "../" + arg
+      if ((arg.endsWith(".scala") || arg.endsWith(".java")) && !(new File(arg)).isAbsolute) ".." + sep + arg
       else arg
     }
     storeCompileOptions(args2)
@@ -61,9 +64,10 @@ object Bench {
     val libs = if (args.contains("-with-compiler")) compiler_libs else standard_libs
     var argsNorm = args.filter(_ != "-with-compiler")
 
+    import File.{ pathSeparator => sep }
     var cpIndex = argsNorm.indexOf("-classpath")
     if (cpIndex == -1) cpIndex = argsNorm.indexOf("-cp")
-    if (cpIndex != -1) argsNorm(cpIndex + 1) = argsNorm(cpIndex + 1) + java.io.File.pathSeparator + libs
+    if (cpIndex != -1) argsNorm(cpIndex + 1) = argsNorm(cpIndex + 1) + sep + libs
     else argsNorm = argsNorm :+ "-classpath" :+ libs
 
     val file = new File(COMPILE_OPTS_FILE)
diff --git a/compiler/src/dotty/tools/dotc/classpath/DirectoryClassPath.scala b/compiler/src/dotty/tools/dotc/classpath/DirectoryClassPath.scala
index a761d746efdd..73702947a991 100644
--- a/compiler/src/dotty/tools/dotc/classpath/DirectoryClassPath.scala
+++ b/compiler/src/dotty/tools/dotc/classpath/DirectoryClassPath.scala
@@ -174,7 +174,7 @@ final class JrtClassPath(fs: java.nio.file.FileSystem) extends ClassPath with No
     if (inPackage == "") Nil
     else {
       packageToModuleBases.getOrElse(inPackage, Nil).flatMap(x =>
-        Files.list(x.resolve(inPackage.replace('.', '/'))).iterator().asScala.filter(_.getFileName.toString.endsWith(".class"))).map(x =>
+        Files.list(x.resolve(FileUtils.dirPath(inPackage))).iterator().asScala.filter(_.getFileName.toString.endsWith(".class"))).map(x =>
         ClassFileEntryImpl(new PlainFile(new dotty.tools.io.File(x)))).toVector
     }
   }
@@ -193,7 +193,7 @@ final class JrtClassPath(fs: java.nio.file.FileSystem) extends ClassPath with No
     else {
       val inPackage = packageOf(className)
       packageToModuleBases.getOrElse(inPackage, Nil).iterator.flatMap{x =>
-        val file = x.resolve(className.replace('.', '/') + ".class")
+        val file = x.resolve(FileUtils.dirPath(className) + ".class")
         if (Files.exists(file)) new PlainFile(new dotty.tools.io.File(file)) :: Nil else Nil
       }.take(1).toList.headOption
     }
@@ -207,7 +207,7 @@ case class DirectoryClassPath(dir: JFile) extends JFileDirectoryLookup[ClassFile
 
   def findClassFile(className: String): Option[AbstractFile] = {
     val relativePath = FileUtils.dirPath(className)
-    val classFile = new JFile(s"$dir/$relativePath.class")
+    val classFile = new JFile(dir, relativePath + ".class")
     if (classFile.exists) {
       val wrappedClassFile = new dotty.tools.io.File(classFile.toPath)
       val abstractClassFile = new PlainFile(wrappedClassFile)
@@ -232,7 +232,7 @@ case class DirectorySourcePath(dir: JFile) extends JFileDirectoryLookup[SourceFi
   private def findSourceFile(className: String): Option[AbstractFile] = {
     val relativePath = FileUtils.dirPath(className)
     val sourceFile = Stream("scala", "java")
-      .map(ext => new JFile(s"$dir/$relativePath.$ext"))
+      .map(ext => new JFile(dir, relativePath + "." + ext))
       .collectFirst { case file if file.exists() => file }
 
     sourceFile.map { file =>
diff --git a/compiler/src/dotty/tools/dotc/classpath/FileUtils.scala b/compiler/src/dotty/tools/dotc/classpath/FileUtils.scala
index 684fc7a58239..a8628be6db3c 100644
--- a/compiler/src/dotty/tools/dotc/classpath/FileUtils.scala
+++ b/compiler/src/dotty/tools/dotc/classpath/FileUtils.scala
@@ -43,7 +43,7 @@ object FileUtils {
     else throw new FatalError("Unexpected source file ending: " + fileName)
   }
 
-  def dirPath(forPackage: String): String = forPackage.replace('.', '/')
+  def dirPath(forPackage: String): String = forPackage.replace('.', JFile.separatorChar)
 
   def endsClass(fileName: String): Boolean =
     fileName.length > 6 && fileName.substring(fileName.length - 6) == ".class"
diff --git a/compiler/src/dotty/tools/dotc/classpath/VirtualDirectoryClassPath.scala b/compiler/src/dotty/tools/dotc/classpath/VirtualDirectoryClassPath.scala
index 1579e70afc55..ae285f80790b 100644
--- a/compiler/src/dotty/tools/dotc/classpath/VirtualDirectoryClassPath.scala
+++ b/compiler/src/dotty/tools/dotc/classpath/VirtualDirectoryClassPath.scala
@@ -24,7 +24,7 @@ case class VirtualDirectoryClassPath(dir: VirtualDirectory) extends ClassPath wi
 
   protected def emptyFiles: Array[AbstractFile] = Array.empty
   protected def getSubDir(packageDirName: String): Option[AbstractFile] =
-    Option(lookupPath(dir)(packageDirName.split('/'), directory = true))
+    Option(lookupPath(dir)(packageDirName.split(java.io.File.separator), directory = true))
   protected def listChildren(dir: AbstractFile, filter: Option[AbstractFile => Boolean] = None): Array[F] = filter match {
     case Some(f) => dir.iterator.filter(f).toArray
     case _ => dir.toArray
@@ -41,7 +41,7 @@ case class VirtualDirectoryClassPath(dir: VirtualDirectory) extends ClassPath wi
 
   def findClassFile(className: String): Option[AbstractFile] = {
     val relativePath = FileUtils.dirPath(className) + ".class"
-    Option(lookupPath(dir)(relativePath split '/', directory = false))
+    Option(lookupPath(dir)(relativePath.split(java.io.File.separator), directory = false))
   }
 
   private[dotty] def classes(inPackage: String): Seq[ClassFileEntry] = files(inPackage)
diff --git a/compiler/src/dotty/tools/dotc/classpath/ZipArchiveFileLookup.scala b/compiler/src/dotty/tools/dotc/classpath/ZipArchiveFileLookup.scala
index 256956fdb54b..42226e9a3b8f 100644
--- a/compiler/src/dotty/tools/dotc/classpath/ZipArchiveFileLookup.scala
+++ b/compiler/src/dotty/tools/dotc/classpath/ZipArchiveFileLookup.scala
@@ -66,7 +66,7 @@ trait ZipArchiveFileLookup[FileEntryType <: ClassRepresentation] extends ClassPa
   }
 
   private def findDirEntry(pkg: String): Option[archive.DirEntry] = {
-    val dirName = s"${FileUtils.dirPath(pkg)}/"
+    val dirName = pkg.replace('.', '/') + "/"
     archive.allDirs.get(dirName)
   }
 
diff --git a/compiler/src/dotty/tools/dotc/consumetasty/ConsumeTasty.scala b/compiler/src/dotty/tools/dotc/consumetasty/ConsumeTasty.scala
index 6fd80cbe50e2..2e54866459be 100644
--- a/compiler/src/dotty/tools/dotc/consumetasty/ConsumeTasty.scala
+++ b/compiler/src/dotty/tools/dotc/consumetasty/ConsumeTasty.scala
@@ -17,7 +17,8 @@ object ConsumeTasty {
     }
 
     val currentClasspath = QuoteDriver.currentClasspath
-    val args = "-from-tasty" +: "-classpath" +: s"$classpath:$currentClasspath" +: classes
+    import java.io.File.{ pathSeparator => sep }
+    val args = "-from-tasty" +: "-classpath" +: s"$classpath$sep$currentClasspath" +: classes
     (new Consume).process(args.toArray)
   }
 }
diff --git a/compiler/src/dotty/tools/dotc/quoted/QuoteDriver.scala b/compiler/src/dotty/tools/dotc/quoted/QuoteDriver.scala
index faf48ae9e966..827e9d424bb2 100644
--- a/compiler/src/dotty/tools/dotc/quoted/QuoteDriver.scala
+++ b/compiler/src/dotty/tools/dotc/quoted/QuoteDriver.scala
@@ -96,7 +96,8 @@ object QuoteDriver {
       case cl: URLClassLoader =>
         // Loads the classes loaded by this class loader
         // When executing `run` or `test` in sbt the classpath is not in the property java.class.path
-        val newClasspath = cl.getURLs.map(_.getFile())
+        import java.nio.file.Paths
+        val newClasspath = cl.getURLs.map(url => Paths.get(url.toURI).toString)
         newClasspath.mkString("", java.io.File.pathSeparator, if (classpath0 == "") "" else java.io.File.pathSeparator + classpath0)
       case _ => classpath0
     }
diff --git a/doc-tool/src/dotty/tools/dottydoc/staticsite/Site.scala b/doc-tool/src/dotty/tools/dottydoc/staticsite/Site.scala
index 523f9ebe94ce..1e656ee4f37d 100644
--- a/doc-tool/src/dotty/tools/dottydoc/staticsite/Site.scala
+++ b/doc-tool/src/dotty/tools/dottydoc/staticsite/Site.scala
@@ -8,6 +8,7 @@ import java.io.{ File => JFile, OutputStreamWriter, BufferedWriter, ByteArrayInp
 import java.util.{ List => JList, Arrays }
 import java.nio.file.Path
 import java.nio.charset.StandardCharsets
+import java.io.File.{ separator => sep }
 
 import com.vladsch.flexmark.parser.ParserEmulationProfile
 import com.vladsch.flexmark.parser.Parser
@@ -166,9 +167,9 @@ case class Site(
   private def defaultParams(pageLocation: JFile, additionalDepth: Int = 0): DefaultParams = {
     val pathFromRoot = stripRoot(pageLocation)
     val baseUrl: String = {
-      val rootLen = root.getAbsolutePath.split('/').length
-      val assetLen = pageLocation.getAbsolutePath.split('/').length
-      "../" * (assetLen - rootLen - 1 + additionalDepth) + "."
+      val rootLen = root.toPath.toAbsolutePath.normalize.getNameCount
+      val assetLen = pageLocation.toPath.toAbsolutePath.normalize.getNameCount
+      "../" * (assetLen - rootLen + additionalDepth) + "."
     }
 
     DefaultParams(
@@ -197,16 +198,16 @@ case class Site(
         // Suffix is index.html for packages and therefore the additional depth
         // is increased by 1
         val (suffix, offset) =
-          if (e.kind == "package") ("/index.html", -1)
+          if (e.kind == "package") (sep + "index.html", -1)
           else (".html", 0)
 
         val path = if (scala.util.Properties.isWin)
           e.path.map(_.replace("<", "_").replace(">", "_"))
-        else 
+        else
           e.path
-        val target = mkdirs(fs.getPath(outDir.getAbsolutePath +  "/api/" + path.mkString("/") + suffix))
+        val target = mkdirs(fs.getPath(outDir.getAbsolutePath +  sep + "api" + sep + path.mkString(sep) + suffix))
         val params = defaultParams(target.toFile, -1).withPosts(blogInfo).withEntity(Some(e)).toMap
-        val page = new HtmlPage("_layouts/api-page.html", layouts("api-page").content, params, includes)
+        val page = new HtmlPage("_layouts" + sep + "api-page.html", layouts("api-page").content, params, includes)
 
         render(page).foreach { rendered =>
           val source = new ByteArrayInputStream(rendered.getBytes(StandardCharsets.UTF_8))
@@ -223,9 +224,9 @@ case class Site(
       }
 
       // generate search page:
-      val target = mkdirs(fs.getPath(outDir.getAbsolutePath +  "/api/search.html"))
+      val target = mkdirs(fs.getPath(outDir.getAbsolutePath + sep + "api" + sep + "search.html"))
       val searchPageParams = defaultParams(target.toFile, -1).withPosts(blogInfo).toMap
-      val searchPage = new HtmlPage("_layouts/search.html", layouts("search").content, searchPageParams, includes)
+      val searchPage = new HtmlPage("_layouts" + sep + "search.html", layouts("search").content, searchPageParams, includes)
       render(searchPage).foreach { rendered =>
         Files.copy(
           new ByteArrayInputStream(rendered.getBytes(StandardCharsets.UTF_8)),
diff --git a/project/Build.scala b/project/Build.scala
index d616430f56fc..e77c731cd370 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -628,8 +628,7 @@ object Build {
         val dottyLib = jars("dotty-library")
 
         def run(args: List[String]): Unit = {
-          val sep = File.pathSeparator
-          val fullArgs = insertClasspathInArgs(args, s".$sep$dottyLib$sep$scalaLib")
+          val fullArgs = insertClasspathInArgs(args, List(".", dottyLib, scalaLib).mkString(File.pathSeparator))
           runProcess("java" :: fullArgs, wait = true)
         }
 
@@ -645,7 +644,7 @@ object Build {
           val asm = findLib(attList, "scala-asm")
           val dottyCompiler = jars("dotty-compiler")
           val dottyInterfaces = jars("dotty-interfaces")
-          run(insertClasspathInArgs(args1, s"$dottyCompiler:$dottyInterfaces:$asm"))
+          run(insertClasspathInArgs(args1, List(dottyCompiler, dottyInterfaces, asm).mkString(File.pathSeparator)))
         } else run(args)
       },
 
@@ -1092,8 +1091,8 @@ object Build {
       Developer(
         id = "liufengyun",
         name = "Liu Fengyun",
-        email = "liufengyun@chaos-lab.com",
-        url = url("http://chaos-lab.com")
+        email = "liu@fengy.me",
+        url = url("https://fengy.me")
       ),
       Developer(
         id = "nicolasstucki",