Scissor sharpener from Fiskars.
We do not recommend using this sharpener for your best, most expensive fabric shears; it might be worth taking those to a professional knife sharpener. However, for "regular" fabric shears, kitchen scissors, and other types of scissors, a few "clips" in this sharpener can significantly improve their cutting ability, allowing them to cut things they couldn't cut before.
We have tested it ourselves and can confirm that it helps with dull scissors.