Not quite a proxy server, but similar functions with a little less configuration required for end clients:
- PiHole: Extremely popular drop-in to block Ads and Spyware.
- PiHole Blocklists: Github projects with various pre-compiled blocklists
- BlockWorkr: Unified blocklist service.
- DNSWarden Blocklist: DNS blocklist - no longer maintains, but could be good starting point.
- E2Guardian: Successor of Dansgaurdian, which I had good success filtering most “inappropriate” content for K12
In K12 environments, user accounts and authentications are generally useful to provide a method to control who has internet access. Captive portals could represent a nice way to provide this type of
- OpenWRT Captive Portal Docs
- http://www.andybev.com/index.php/Using_iptables_and_PHP_to_create_a_captive_portal: Simple method for captive portal, using iptables and php