A crossbow that mounts on your AR-15 lower.
From the Precision Shooting Equipment website:
Precision-built performance, ground breaking engineering, and a revolutionary concept... Introducing the new TAC 15™ Crossbow by PSE. Forget everything you thought you knew about crossbows, the TAC 15™ sets new standards for accuracy, performance and shootability.
A marvel of innovation and engineering, only PSE could bring you the new TAC 15™. Designed to fit on any AR-15 lower receiver, the TAC 15™ is packed with innovative features that will have to be experienced to be believed. It all starts by incorporating the incredibly strong X Tech™ limbs into an extremely compact platform. The ultra-high performance twin-cam design shoots an amazing 412 fps and is capable of unprecedented accuracy. Plus, the TAC 15™ converts any AR-15 quickly and easily from a gun to a crossbow!
It's awful pricey, but way tacti-cool. Check out the video here.
H/T to Tactical-Life.com