The warp-weighted loom was the first loom and uses tree branches as the harness shafts. The warp ends of yarn are tied to the tree branches and weighted on the ground with rocks or other weights. Because of the simplicity of the loom, the harness shafts can not be raised to create a shed in the warp. Weaving is done on warp-weighted looms by lifting and lowering one thread at a time.
The counterbalance loom uses a treadle, or foot pedal, to lift the harness shafts. You can open a small or large shed depending on the touch of the treadle. Most counterbalance looms have 4 shafts, but they can commonly range from 2 to 10 shafts. This allows you to weave the normal 3 shafts against 1, or any proportion you please. Counterbalance looms also allow you to easily adjust the height of the harness shafts so you can adjust the tension in the warp.
The countermarch loom uses a treadle to raise and lower the harness shafts. It has an extra set of lamms, or pieces of wood the yarn is tied to, which allows for extra tension in the warp. The countermarch loom allows you to add any number of harness shafts to the loom frame, making it ideal for those who want to more than the standard 4 harness shafts.
The jack loom uses a jack, or a piece of wood that is woven into the warp, to create a shed in the warp. The harness shafts stay still, making this an inexpensive loom option. The harness shafts are placed a couple inches lower than other looms and are heavier so that they do not break under the tension caused by the jack. The standard jack loom has 4 harness shafts.
A drawloom is a two-harness loom that is used to create repeat patterns in cloth. The first harness can have 4 to 6 harness shafts. The second harness can have from 10 to 100 harness shafts. The harness are fixed with a set of pull handles that are attached to the yarn, which is threaded to weave an area of repeat.
Table looms are similar to jack looms, but are much smaller. The harness shafts are small and often have springs below to help hold them down. Weaving is done using a jack because table looms do not have treadles so the harness shafts are still.