diff --git a/bin/serveit b/bin/serveit
new file mode 100755
index 0000000..77f4f37
--- /dev/null
+++ b/bin/serveit
@@ -0,0 +1,203 @@
+#!/usr/bin/env ruby
+
+require "find"
+require "webrick"
+require "open3"
+require "optparse"
+
+class ServeIt
+  VERSION = [0, 0, 1]
+  def self.main
+    serve_dir, ignored_paths, command = parse_opts
+    serve_dir = File.expand_path(serve_dir)
+    Server.new(serve_dir, ignored_paths, command).serve
+  end
+
+  def self.parse_opts
+    options = {:serve_dir => ".",
+               :ignored_paths =>  []}
+    parser = OptionParser.new do |opts|
+      opts.banner = "Usage: #{$PROGRAM_NAME} [options] command"
+      opts.on_tail("-s", "--serve-dir DIR", "Root directory for server") do |dir|
+        options[:serve_dir] = dir
+      end
+      opts.on_tail("-i", "--ignore PATH", "Ignore changes to file or directory") do |path|
+        options[:ignored_paths] << path
+      end
+      opts.on_tail("--version", "Show version") do |dir|
+        puts ServeIt::VERSION.join('.')
+        exit
+      end
+    end
+
+    begin
+      parser.parse!(ARGV)
+    rescue OptionParser::InvalidOption => e
+      $stderr.puts e
+      $stderr.puts parser
+      exit 1
+    end
+
+    if ARGV.count == 0
+      command = nil
+    elsif ARGV.count == 1
+      command = ARGV.fetch(0)
+    else
+      $stderr.write parser.to_s
+      exit 1
+    end
+
+    [options.fetch(:serve_dir), options.fetch(:ignored_paths), command]
+  end
+
+  class Server
+    def initialize(serve_dir, ignored_paths, command)
+      @mutex = Mutex.new
+      @serve_dir = serve_dir
+      @command = command
+      @rebuilder = Rebuilder.new(@command, ignored_paths) if @command
+    end
+
+    def serve
+      port = 8000
+      puts "Starting server at http://localhost:#{port}"
+      server = WEBrick::HTTPServer.new(:Port => port)
+
+      server.mount_proc '/' do |req, res|
+        relative_path = req.path.sub(/^\//, '')
+        local_abs_path = File.absolute_path(relative_path, @serve_dir)
+
+        if relative_path == "favicon.ico"
+          respond_to_favicon(res)
+        else
+          respond_to_path(res, relative_path, local_abs_path)
+        end
+      end
+
+      trap 'INT' do server.shutdown end
+      server.start
+    end
+
+    def respond_to_favicon(res)
+      res.status = 404
+    end
+
+    def respond_to_path(res, relative_path, local_abs_path)
+      begin
+        rebuild_if_needed
+      rescue Rebuilder::RebuildFailed => e
+        return respond_to_error(res, e.to_s)
+      end
+
+      if File.directory?(local_abs_path)
+        respond_to_dir(res, relative_path, local_abs_path)
+      else
+        # We're building a file
+        respond_to_file(res, local_abs_path)
+      end
+    end
+
+    def respond_to_error(res, message)
+      res.content_type = "text/html"
+      res.body = "<pre>" + message + "</pre>"
+    end
+
+    def respond_to_dir(res, rel_path, local_abs_path)
+      res.content_type = "text/html"
+      res.body = (
+        "<p><h3>Listing for /#{rel_path}</h3></p>\n" +
+        Dir.entries(local_abs_path).select do |child|
+          child != "."
+        end.sort.map do |child|
+          full_child_path_on_server = File.join("/", rel_path, child)
+          %{<a href="#{full_child_path_on_server}">#{child}</a><br>}
+        end.join("\n")
+      )
+    end
+
+    def respond_to_file(res, local_abs_path)
+      res.body = File.read(local_abs_path)
+      res.content_type = guess_content_type(local_abs_path)
+    end
+
+    def guess_content_type(path)
+      extension = File.extname(path).sub(/^\./, '')
+      WEBrick::HTTPUtils::DefaultMimeTypes.fetch(extension) do
+        "application/octet-stream"
+      end
+    end
+
+    def rebuild_if_needed
+      # Webrick is multi-threaded; guard against concurrent builds
+      @mutex.synchronize do
+        if @rebuilder
+          @rebuilder.rebuild_if_needed
+        end
+      end
+    end
+  end
+
+  class Rebuilder
+    def initialize(command, ignored_paths)
+      @command = command
+      @ignored_paths = ignored_paths
+      @last_disk_state = nil
+    end
+
+    def rebuild_if_needed
+      if disk_state != @last_disk_state
+        stdout_and_stderr, success = rebuild
+        if !success
+          message = "Failed to build! Command output:\n\n" + stdout_and_stderr
+          raise RebuildFailed.new(message)
+        end
+
+        # Get a new post-build disk state so we don't pick up changes made during
+        # the build.
+        @last_disk_state = disk_state
+        [stdout_and_stderr, success]
+      end
+    end
+
+    def rebuild
+      puts "Running command: #{@command}"
+      puts " begin build".rjust(80, "=")
+      start_time = Time.now
+      stdout_and_stderr, status = Open3.capture2e(@command)
+      print stdout_and_stderr
+      puts (" built in %.03fs" % (Time.now - start_time)).rjust(80, "=")
+      [stdout_and_stderr, status.success?]
+    end
+
+    def disk_state
+      start_time = Time.now
+      paths = []
+
+      Find.find(".") do |path|
+        if ignore_path?(path)
+          Find.prune
+        else
+          paths << path
+        end
+      end
+
+      paths.map do |path|
+        [path, File.stat(path).mtime.to_s]
+      end.sort.tap do
+        puts (" scanned in %.03fs" % (Time.now - start_time)).rjust(80, "=")
+      end
+    end
+
+    def ignore_path?(path)
+      @ignored_paths.any? do |ignored_path|
+        File.absolute_path(path) == File.absolute_path(ignored_path)
+      end
+    end
+
+    class RebuildFailed < RuntimeError; end
+  end
+end
+
+if __FILE__ == $PROGRAM_NAME
+  ServeIt.main
+end