Something that allowed communities to run their own variation of a given tabletop RPG would be really cool.
Character sheet with configurable fields
RPG items (money, gear, consumables, spells, whatever) can be sold in the member shop
Purchased items show as "inventory" on the character sheet
Admins or moderators can "gift" items to characters
Gaming happens by whatever mechanism the community owner prefers (forums or pages database comments)
Something along those lines would be epic.