A lot of companies make an appendix carry holster, but sootch00 makes an argument that the usgruntgear.com makes the best for his Glocks. They also make this holster for the Smith & Wesson M&P series, but it looks like you’re out of luck at the moment if you carry anything else.

I have to confess that I like the simple, rugged nature of the design, and hope that they get around to designing a variant for the Springfield Armory XD series.