Kings of War is a great fantasy rules set from Mantic Games. Here’s a variant for Rome’s Rise and Fall.
Trierarch is a set of free wargames rules for naval warfare in the classical era. The game is based on DBA, with measurements expressed as “ship lengths.”
Civitates Bellantes is a set of free wargames rules for ancient warfare.
From the author:
Civitates Bellantes is an adaptation of the Comitatus mehcanisms to cover the entire era of ‘classical’ antiquity (500 BC-AD 200). These are still a work in progress and I am developing them together with Caoimhín Boru.
Although these rules are designed around the same principles as Comitatus, they also have unique features which capture the flavour of the period. Civitates is suitable for ‘epic’ classical battles using any figure scale or base sizes. A unique feature of the rules is the treatment of a full legion as a single unit with the ability to conduct line relief.
Corvus on Land is a set of free wargames rules to accompany the Richard Lee’s CORVUS (or any other Ancient Naval rules) when played in 1/1200 or smaller scales.
Ross Macfarlane offers A Gathering of Hosts, an ancients wargame. Ross writes:
This is a set of simple rules for playing wargames with toy soldiers depicting ancient warriors. It is not a detailed, simulation of low level ancient tactics or high level ancient command, nor is it intended to be a clever vehicle for challenging competition style games. It is, hopefully, a relaxed game where the gamer can focus on his over all plan, not minor tactical details while getting enough flavour to feel right at a high level.