AdCycle

Adcycle is a free shareware, mySQL-powered online ad management software package for smaller websites.

Features, from the website:

IP/Page/Keyword targeting capability
high performance daemon option
rich media delivery
impression and click frequency capping
campaign priority control
UNIX,NT,98,95 support
campaign grouping
creative priority control
cache bust code/ssi support
click/impression campaigns
timed delivery
multiple banners per campaign
day of week/hour of day control
advertiser reports/login

Seems to be a bit dated, but it's free to check out. I'd pass, though.

Visit Adcycle - ad management software powered by mySQL