If by 'Simple' your goal is to serve static web pages (ie, no support for php, cgi, or fancy stuff), then I switch recently to Fenix web server (Nodejs based I think), (I found it after being fed up with encoding issues on Windows with Python SimpleHttpServer)

• super easy to start (I even suggest it for non developers given how easy it is),
• works on Windows and OsX
• gives you support to localtunnel, which enables you to share your local content with someone that is not even on your network (the url will only be valid for a limited time, but it's very handy to share progress while working remotely)
• free and open source (GPL)

fenixwebserver.com

Since I gave it a try, I haven't switched to anything else (unless need for more, in which case I'm more using Docker container in VMs, so that you have the same configuration no mater the host)

BrowserSync.io is a very simple solution. Install it globally and run a simple command to start a static HTML web server on any platform.

I use python -m SimpleHTTPServer 8000 on my mac. For windows you can either download & install Mongoose or use Cygwin/ActivePython.

Basic and yet useful python -m SimpleHTTPServer <PORT>