Some houserules for GURPS. They were written about 10 years ago, so they're quite old and possibly outdated by changes which have been released since then (especially 4th Edition, which is due out soon at the time of writing).

		
		    There's a 4th Edition take on GURPS Metric
			

here - which is more general purpose.

For a science fiction campaign I was running, I needed to design some spaceships. However, neither GURPS Space nor GURPS Vehicles were quite right. The latter had the right level of complexity, but it didn't use the metric system. If I'm designing spacecraft, I don't want to work with miles per hour.

So I converted GURPS Vehicles to the metric system, and modified the technology along the way (I wanted a Hard SF campaign, so there are no reactionless drives until very high TLs).

GURPS Metric -