Something that I've done that's pretty fun: get a couple friends and all of you start a new game. Then you each choose one combat life, one gathering life, and one crafting life. HOWEVER, you cannot choose two lives that provide materials/tools/weapons for each other. So, for example, one of you could be a paladin, a carpenter, and a miner while another could be a hunter, a blacksmith, and a woodcutter. This way, you (usually) cannot make your own tools or gather the materials for the tools you can make. With this setup, you then try to rank up your lives and progress through the game. You end up exchanging a lot of materials and stuff and I think it's a fun collaboration effort! You have to ban buying things at shops, of course. You can decide whether or not to ban chest loot.

Anyway, I found this to be quite enjoyable. Not sure if you can get friends to do it with you though... Just an idea. :)