Welcome. You don't need a dedicated ruleset to play any RPG via FG. You can use the included CoreRPG rulset to make your own character sheets etc as with these examples; https://www.fantasygrounds.com/forum...aracter-Sheets
Or are viresanimi points out, you can use the community MoreCore ruleset that has advanced capabilities and specialty roles like those for CoD; https://www.fantasygrounds.com/forum...reCore-Ruleset