Rigid heddle is an ancient Scananavian weaving implement originally designed to weave narrow bands. The rigid heddle, itself, is not a loom. The rigid heddle is merely a shedding device. It takes the place of string heddles and a shed rod (often seen in backstrap weaving). Anything that holds warp under tension is a loom. You can use rigid heddles on anything that holds warp under tension.
With today's really wide rigid heddles (up to 32" in some cases) and the frames with "shed blocks" which hold the sheds open, this bit of history about the rigid heddle is becoming lost or is not made known to the people using them.
Here's Susan Foulkes to bring us back to basics with the original intended use for the rigid heddle. There are several articles on this blog relating to narrow bands. Search the site for "inkle" for instructions and patterns.