NNTPCache is Squid for news (plus lots more).

NNTPCache (very efficiently, using shared memory, COW, mmaps, etc)
executes on the localhost pretending to be an NNRP news reading
server. In fact, what it does is pass certain NNTP commands through
to real (remote and possibly local) news-servers based on various
pattern matching rules. nntpcache then takes the output from those
servers and caches & indexes it in funky ways (much specific case
magic goes into this).  The next time such information is asked
for, or other information which can be logically inferred from the
previously collated information, it is sent directly from the cache,
without consulting the remote servers. NNTPCache can transparently
merge multiple servers, (permiting local newsgroups with remote
NNTP feeds), filter articles, xovers, and headers based on weighted
regular expressions, and has built in NoCem/PGP (anti-spam) support
(see http://www.nocem.org/ for details).

WWW: http://www.nntpcache.com/