ReSlice - Slice your audio with an advanced, rhythmic arpeggiator and FX.
Songstack - Swipe to discover new music for Spotify
cassini - Polyphonic Synthesizer for iPhone/iPod touch
mixmello - mixmello is a free, open source tool to create remixed versions of your favourite playlists.
nlog Synth - Professional Virtual Analogue Synthesizer ::: check nlogmusic at YouTube :::
Music Walker - Explore and play (via YouTube) songs similar to a seed song.