Squid is a fully-featured HTTP/1.0 proxy with partial HTTP/1.1 support
The 7 series brings many new features and upgrades to the basic
networking protocols. A short list of the major new features is:

Squid 7 represents a new feature release, the most important of these
new features are:

 * better support for overlapping IP ranges and wildcard domains in acl
 * countless security, portability, and documentation fixes

Since version 6, some previously deprecated features have been removed:
 * Edge Side Includes (ESI)
 * access to the cache manager using the cache_object://
   scheme - use http instead
 * the squidclient tool - use curl
   http://<squid-address>/squid-internal-mgr/menu instead
 * the cachemgr.cgi tool
 * the purge tool - use the http PURGE method instead
 * Ident protocol support
 * basic_smb_lm_auth and ntlm_smb_lm_auth helpers - use
   Samba's ntlm_auth instead