When comparing Open d6 vs Risus, the Slant community recommends Risus for most people. In the question“What are the best tabletop RPGs?” Risus is ranked 12th while Open d6 is ranked 22nd. The most important reason people chose Risus is:
Risus has a very minimalist rule system that breaks down all actions to their core function. Risus comes with a super short, four page rulebook (available in many forms and formats) that's easy to read, includes examples and has a bit of humor thrown in to make the process or learning more enjoyable.
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Pros
Pro Includes rulebooks covering the more common genres
Open d6 includes rulebooks for Fantasy, Adventure and Space settings.
Pro No special dice required
The game can be played with common six-sided dice.
Pro A simplified variant, called Mini Six, is available
Mini Six is a fan-made variant of Open d6 that aims to be a distilled version of the Open d6 system.
Pro There are theme-related books available to start various types of games
D6 Space is West End Games old "Star Wars D6" game with all of the licensed Star Wars names removed. It's a stand alone complete game.
D6 Fantasy is a standalone ruleset for running a D&D type game with the D6 system.
D6 Adventure is a standalone ruleset for using the D6 system in a Wild West, spies, or modern adventure game.
All three have supplement books (Spaceship design, magic, aliens, etc).
Pro Each rulebook has a good introductory section
Pro Can be taught in less than 10 minutes
Risus has a very minimalist rule system that breaks down all actions to their core function. Risus comes with a super short, four page rulebook (available in many forms and formats) that's easy to read, includes examples and has a bit of humor thrown in to make the process or learning more enjoyable.
Pro Very flexible rules
Risus is not confined to a selection of pre-defined character-classes, settings or abilities. Characters are described via clichés such as Witch Doctor, Gambler, Musician with a number of dice assigned to each cliché that are then used in challenges that relate to the appropriate cliché.
Pro A large following that provides a lot of content
A large amount of adventures, artwork, characters, clichés as well as optional rules can be found for Risus. An excellent resource for all aforementioned things as well as many others is Risusiverse, a fan-made website of all things Risus.
Cons
Con Complicated magic system
Con Little guidance can be found for GMs and players
Some prior understanding of how an RPG is played and what is the role of the GM is required as the rules cover only the very core of the system.