At the risk of being selfish...
A standalone/downloadable version.
Not everyone has a laptop to drag to a game, not everyone has a computer that's easily accessible for game time, and outside the U.S., (like say here in NZ) you have data limits. Go over X amount and either you pay more, or your connection gets capped (hello dialup). And of course, there _are_ folks that don't have broadband accounts for a variety of reasons too.
Also as a practical aspect... let's face it, when you've got a hosted program, eventually... it's going to go away. You'll get bored maintaining it, something will happen with the hosting... whatever. Nothing is forever.
A downloadable version though, means that even when life has come up and you just can't work on it for [whatever] reason, or you're bored with it, or whatever, at least folks can still benefit from the work you put into this thing.
Just something to consider.
NPC Designer might fit your needs if you are using windows and want offline