Squis is a fully-featured HTTP/1.0 proxy which is almost (but not quite - we're getting there!) a fully-featured HTTP/1.1 proxy. Squid offers a rich access control, authorization and logging environment to develop web proxy and content serving applications. Squid offers a rich set of traffic optimization options, most of which are enabled by default for simpler installation and high performance.

Squid 4 represents a new feature release above 3.5.

The most important of these new features are:

Configurable helper queue size
Helper concurrency channels changes
SSL support removal
MSNT-multi-domain helper removal
Secure ICAP
Elliptic Curve Diffie-Hellman (ECDH)
Improved SMP support