Base Project Source Control

Hi,

I'm trying to find out about any available source control software, which in particular has the ability to handle multiple projects based on a single project.
In other words, a set of base code which has multiple child projects derived from it, where any changes to the base code will filter through to those child projects.

I've been using MS SourceSafe 6 for quite a number of years now, and am aware of sharing/branching... but it's messy, and I wondered if there were any other well known and respected applications out there?

After a bit of research, I'm nowhere nearer a conclusion, and any suggestions and/or advise would be very welcome.

Many thanks,
Tom