Hi,

is there any use for gems in the game other than selling for money?

What about rings i have found that have no effect in their description? Only for sale as well?

Some people used gems for lighting in their home base at night. In general, though, gems and rings without stats are only good for trade.
You may want to sell the higher weight/value items first, such as equipment, and keep gems and jewellery as the next best trade item to gold, in cases where you can not (or don't want to) leave and return (to get items for trade from a stash).