I've used the XtremeWorlds software before, but than I switched to Eclipse when spam bots raided XW :D never really used XW since. XW is a good software, but Eclipse just offers so much more, unless you count the fact that XW acually comes with a quest system :D
I'm pretty experienced with MMO design in general so here's something I've found out: almost all MMO engines are programmed in VB6 and are based off the mirage realms source code. I plan to change this once I learn enough C++ and make a C++ MMORPG engine :D No idea for the name yet so it'd help if somebody had some ideas. If you can use engine A, you can use engine B just as well, it'll take some adjusting but everything is a lot the same.