A challenge could be a title or topic based writing, using a specific song form or song forms, using specific writing techniques, composition, arrangement... even music promotion challenges, all aimed at expanding your skills and knowledge base.
New trial forums for rappers... it is a parental advisory board, so you need to be a member to gain access.
Submit battles, search battles, respond to battles etc.
Battles can be different in many ways, lyrics only, recorded, no cursing, max lines and so on, whoever starts the battle determines the rules of the battle and states it before an opponent accepts the challenge.
Leaderboards may be made for weekly/monthly/all time scores.