Harvester guilds: collecting mats and selling them to other homins
Crafter guilds: buying mats and concentrating on crafting equipment
Merchant guilds: travelling across the lands to buy & sell different races equipment.
Pathfinder guilds: escorting people from one place to another like for example Pyr-Thesos. Doing it in a "shuttle" way.
These are just a few ideas i had, they could be interesting for someone who's wondering what guild he could start and is hesitating

Feel free to comment, or find something else, but don't forget it's just something that crossed my mind between 2 kills and might be totally utopic
