Tape Cassette 2 is an audio plugin that emulates the warmth, noise and character of old tape cassettes. More info and download.
Get lots of free samples/patchs for iOS apps or as Wav files from Electronicsounds (Donations possible).
Caustic 3 is a music creation tool inspired by rack-mount synthesizers / samplers rigs. Everything is real-time and optimized for mobile devices.
But the desktop version is free (No support)