We have a Guild in Sirion (East Continent) for something like training matches. We also have the E.C.D.A., a larger guild in many places dedicated to interaction among the nobles of different realms with the excuse that it's sole to discuss about drinks and beverages.
I had a Secrec Society in Sirion during the Great War, to gather the military minds and discuss the plans and orders in a time of too much fear of spies. About Infiltrators and Adventurers, many realms have this kind of guilds.