While much of the UI is stock Android, some features such as the lock screen, almost look like they have been taken from CyanogenMod. Also added are quick setting toggles in the notification bar. Outside of those two things, the rest of the phone has pretty much all of the things you would expect from an entry-level Android device, including access to the Android Market.
It sounds like an interesting idea even though Republic Wireless could ask you not to return if your non Wi-Fi usage exceeds 550 minutes of calls, 150 texts and 300MB of data monthly. Especially with the latter "informal cap" on data usage, power users might want to stay away from the carrier. On the other hand, casual users just might be able to save a lot of money using Republic Wireless as long as they don't mind being locked into one specific phone.