The McLaren Synth Kit (at https://github.com/mclarenlabs/libs-mclaren-alpha) is an Objective-C toolkit for building projects that simplify working with MIDI and sound synthesis on Linux. We open-sourced it last year and have been refining it with new features and capabilities.

We've been inspired to be creators ever since we got our first Raspberry Pi.  It makes possible so much invention and experimentation for not a lot of money.  One of the things we've wanted is an easy-to-use, dead simple tone generator for using the Raspberry Pi as a MIDI instrument.
Our just-released Organ synthesizer makes it easy for anyone to get started with using a Raspberry Pi as a musical instrument.  Plug a MIDI keyboard into the USB port and play.  Or grab a MIDI file and experiment with different sounds.  It's fun, and it's easy.  And best of all, it was designed specifically for the Raspberry Pi!