These are all abstraction layers (for each language) which then can be run seamlessly on top of CGI, SCGI, mod_(perl|python|ruby), etc.
- http://plackperl.org
- http://en.wikipedia.org/wiki/Plack_(software)
- http://en.wikipedia.org/wiki/PSGI
- http://en.wikipedia.org/wiki/Wsgi
- http://en.wikipedia.org/wiki/Rack_(web_server_interface)