Does anyone have any ideas on simple art/craft projects for adults?

Buttons sewn or glued onto felt or velour, and then put in a frame sounds simple, but really comes out nice. If the folks can sew, these can also be sewn onto sweaters or t-shirts. Cut out a paper pattern and trace it onto the fabric. Add the buttons. You can get pretty gold and silver ones, at crafts supplies stores in grab bags, that are perfect for this and not very expensive. For the t-shirts, sew a handful of buttons around the neck, maybe make two rows. Around Christmastime, make a large triangle (7" or 8" tall and about 3" or 4" wide at the bottom) on dark green fabric. Put a few dark buttons under it for a trunk, and you have a real work of art. Mine's on a shirt, and it never fails to get comments when I wear it.

You could teach them to do origami - The flapping bird is easy to teach and all you need is some pretty paper but it doesn't take 3 hours... How about teaching them to crochet? A few skeins of yarn could be shared, each person needs a crochet hook. With 3 hours, you could teach them to chain stitch, single crochet, double crochet and their sample could be fashioned into a hot pad.

Try Steve Dodds' book "Re-Creative." It lists 50 crafts to make out of "found items" (i.e. tables made of old wine crates and pizza pans and pillows made out of old neckties), as well as instructions for making them.

Paper Quilling is fun and is not expensive. Great for cards , Christmas ornaments and scrap booking ;))))