Tabletop help ... sorta

So I'm starting to plan this sci-fi tabletop game which features stable wormholes linking locations (think of a less-cheesy version of Stargate: Atlantis or an inferior version of The Algebraist) and I'm wondering if there's some kind of (easy to use and free) mapping programme that anyone knows of to show solar systems and their relationship to each other based on the wormholes?

Any help gratefully received.

The Joy of Wiki

Some days I am so thoroughly entertained by wikipedia that I can spend an entire afternoon chasing links. Eventually one comes up with a gem like this, which is just too good not to share.