The best replacement for fastcgi is cgi.

The best alternatives to fastcgi are rated as following:
★★★★★  cgi
★★★★  suphp
★★★★  isapi
★★★★  mod_php
★★★  mod_perl
★★★  wsgi
★★★  php-fpm
★★★  fcgid
★★  mod php
★★  fcgi
★  fpm
★  isapi php
★  uwsgi
★  mod_python
★  mod perl
★  reverse proxy
★  scgi
★  iis cgi
★  mod fcgid
★  passenger
★  dso
★  apache module
  mod_wsgi
  other cgi
  mod_fcgid
  mod python
  http proxy

Your alternative for fastcgi is not listed? Suggest!
Speaking about fastcgi, one probably shouldn't forget about php.

Other search terms related to fastcgi and their ratings are:
★★★★★ php
★★★ nginx
★★ lighttpd
★ apc
suexec
You have in mind a companion for fastcgi and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of fastcgi in all years. Click on graph for more.
fastcgi
cgi
suphp