AudioSwift is a Mac app that performs the neat trick of turning your laptop’s trackpad into a MIDI controller. Now at version 2, it’s looking more capable than ever.
You can enable AudioSwift with a four- or five-finger tap, and there are five controller modes. Slider lets you send CC or pitchbend messages using virtual faders; XY can be used to control multiple parameters at the same time; Mixer can be called on when you want to adjust levels; Trigger gives you a set of pads for firing off sounds and clips; and Scale lets you play notes in the selected key.
You can download a demo on the AudioSwift website, while the full version costs $24. However, you can currently get the app at a 50% discount using the code GOLDENFROG50.