My comrade Shing02 recently assisted in the development of the SPAT app; it allows you to connect two phones via bluetooth, select an instrumental, spit bars against one another, upload, and then have the community vote on the winner. SPAT also features a solo freestyle mode which allows you to archive your takes. I wholeheartedly believe that this is a great resource for anyone in the rap discipline and also it’s just productive fun!!
Download Link -> https://itunes.apple.com/us/app/id1005035395