Tobias Schlitt has added Akismet support to the PEAR package Services_Trackback, which he writes about here.
PEAR is a “framework and distribution system for reusable PHP components.” It’s used by a lot of PHP developers much like CPAN is for Perl.
Akismet in Pear
Akismet 
Yes, PEAR is great, and unfortunately WordPress is not based on it. When, Matt, when?