The creator of the @garadget has very kindly shared a recipe for building your own DIY version of the Garadget garage door opener, including parts required, onto which you can install the GNU-licensed firmware (or even make changes to it). There is already a binding available for openHAB (1, works on 2) so you can know your home-made device will work with openHAB. Or, you can pre-order a pre-built one. Hooray for open source!
More information here: