A Knitting Harp has uneven peg alignment between the top and bottom rows and produces a single layer fabric.
A Knitting Loom has even peg alignment on the top and bottom rows and produces a double layer or thickness in fabric.
Using a Knitting Rake, which basically 1/2 of a Knitting Loom, produces a single layer fabric as well.
Neither the harp or this brand of loom are adjustable, and the larger gauge requires two strands of worsted weight yarn held together while working a project.
Knitting Harps, Knitting Looms and Knitting Rakes come in all gauges and lengths, you could even make several yourself. It's knitting-without-needles.