I'm no expert - but we will be launching EN World's CAMPAIGN MANAGER soon (it needs testing first) which is designed specifically for that sort of thing - including tracking players, permissions for posting in campaign threads determined by the GM, ability to apply to join games, GMs can accept applications or boot a player, plus character records and campaign information.
It works alongside and interfaces with our existing PbP threads (it doesn't replace them), and can also be used for any other type of game - real life, IRC, virtual tables, etc.