Roar of the Crowd is a set of free rules for playing science fiction, fantasy or historical gladiator games.
Here’s a link to a set of Dr. Who miniatures rules.
Astral Dreams is a free miniatures game based on the d20 Open Gaming License system. The game’s background is based on a short story of the same name, which involves a war between humans and robots.
The folk at One Page Rules have released a new edition of GrimDark Future, a set of one-page rules (with lots of pages of armies you can also download)
Under the Broken Moon is an RPG based on the Thundarr the Barbarian cartoon series. The game uses a mechanic where you roll a number of dice equal to your trait score and sum the results.