Kontakt - With KONTAKT 6, you can sound like a snare drum, a symphony orchestra, or anything in between, from a universe of sampled instruments.
SoundGrail - SoundGrail Music App designed for pianists, guitarists, and DJs.
UVI Falcon - Sampler/synth hybrid instrument
Splice - Music creation, collaboration, and sharing made simple.
Pianoteq - Pianoteq is a virtual piano that runs on your computer.
n-Track Studio - Audio recording and music creation app for iOS.