The best replacement for firewalls is software firewalls.

The best alternatives to firewalls are rated as following:
★★★★★  software firewalls
★★★★  ids
★★★  routers
★★★  hardware firewalls
★★★  proxy servers
★  acls
★  zone based firewalls
★  file security
  windows firewalls

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

Other search terms related to firewalls and their ratings are:
★★★★★ dmz
You have in mind a companion for firewalls and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of firewalls in all years. Click on graph for more.
firewalls
software firewalls
ids