|I used a licensed fork of Perforce at a very large SW company for several years and loved it.
It was lightweight and had a simple command line interface (there are of course gui tools as well), yet was amazingly flexible and powerful.
It simply and without a lot of overhead did what one typically wants from an SCC tool, yet did not present, impose, nor attempt to enforce some pre-conceived notion of development/build/test processes the way a lot of tools do.
One could create enlistments with notepad (edit or create two little files with trivial content and you're done), etc.
Unfortunately, Perforce's cost and licensing model is not terribly affordable or friendly to smaller SW development establishments/houses/companies, or I'd have bought it myself for my employer.
Given that VSS is bundled free and etc, that seems to be what a lot of programs and companies and projects end up with. And for good reason (cost-wise), given what I've seen of the price and licensing models of a lot of the commercial alternatives...