Generate audio in your browser by certain rules with the WoframTones Generator. You can download results in several audio fromats and as well as MIDI files.
This is a nice MIDI controller from Artifon. Not cheap though, 600+. Features:
Play guitar, bass, synth, violin, drum pads, and more, on a revolutionary MIDI controller
TIME Magazine “Best Invention of the Year,” #1 Instrument on Kickstarter, PCMag Editors’ Choice
The first fretted and fretless digital string instrument; low-latency, pressure-sensitive playing
Ultra Portable: Lightweight and 6-Hour Battery Life; USB & Lightning Cable iOS and Mac Connectivity
2 Stereo Speakers & Headphone Jack for creating on your own, or jamming with friends
The Music and Sound Design Platform (also referred to as Music_SDP and MSDP) is free and open-source software built for electronic and electroacoustic music performance, production, improvisation, and experimentation. Music_SDP is a DAPE, or Digital Audio Performance Environment, functioning similarly to a DAW (Digital Audio Workstation), but designed with a special modular structure built for live performances. MSDP provides a non-linear, infinitely expandable, totally hackable, easy-to-use interface for sound design that encourages and rewards exploration and experimentation. It is a great platform for beginners and professionals alike, and provides all the tooling and control needed to make wild new sounds, build complex sonic projects, and execute flawless performances.