Images of Savage Barrel nut and wrench.

Available here: Savage and Remington. Anyone with threading ability and a decent lathe can make one as well as threading the barrel to use it.
There are other companies who sell them. This system can be set up on about any action you want, other than actions that have the locking lugs in the barrel itself. That might/would be more difficult.

http://www.gstprecision.ca/product/savage-barrel-nut-chrome-moly/