I'm with Doc on this. UI-View still seems to be one of the most popular and I certainly enjoyed it. What other choices are there? I was thinking of setting up an iGate with it. What else do iGates use?
You can still use UI-View but you might want to reserve an inexpensive Win XP machine for it. If all you want to do is iGate, you can run APRSPlus: APRSa4 Download files. It's included in the downloads for APRS+SA package. Unfortunately, that software hasn't been updated in a while, either.
I think the software with the most current development is XASTIR, but that's a Linux solution.