Oops - caching proxy server.
Oops! is a proxy server; the main aims of its development being
stable operation, service speed, main protocols support,
modularity, ease at use. What is one more server for when there is
already Squid? I personally was not satisfied with Squid on some
points, that is was why I wished to get rid of it. And that was done.

Basic differences from Squid: 
Each request is served by a separate thread, which allows to use all
available processors on multiprocessor machine. 
Cashed documents are stored in one or several big files. This makes
it possible to remove from the operational system a load on operation
with directories and to speed up access to the documents, and to use
raw-devices as a storage of cashed objects either. 
The program modular structure provides extension of its function
without any change of the source code. 
The special attention was paid to the point of providing a stable,
continuous, unbreakable work, easy and simple
configuration/reconfiguration. Thus, for example, the reconfiguration
on the fly doesn't result in a breakaway of already established connections.

WWW: http://oops-cache.org/oops.eng/