From Physical Audio labs, Derailer is a modeling synth with two elements: a metal bar that you can strike or bow, and a "spring" that lets you join two or more bars together so that vibrations from striking one will affect the other, creating sympathetic resonance. We got clued into it off of Richard Devine's LinkedIn feed, so you know it's tweaky.

It's currently in beta and therefore free to download, the only catch being that you need to have a recent Mac with a "Sandy Lake" or later Intel processor. WIth up to 27 strike bars and five resonators, you can create a lot of truly haunting and interesting soundscapes.

Details, videos, audio examples, and download instructions are here.