When comparing Open d6 vs GRIN, the Slant community recommends Open d6 for most people. In the question“What are the best tabletop RPGs?” Open d6 is ranked 22nd while GRIN is ranked 36th. The most important reason people chose Open d6 is:
Open d6 includes rulebooks for Fantasy, Adventure and Space settings.
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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 Zero dice required
GRIN uses a a standard deck of playing cards instead of dice.
Pro Narrative focus
With no intrusive dice or math players can focus on the story, with every action being resolved by the simple draw of a card.
Pro Creates excellent tension
GRIN uses a a standard deck of playing cards to create a fast paced and deadly feel that evokes modern horror films. One of the best horror games made, its ideal for Halloween or horror movie nights.
Pro Its great for single session games
Like any horror film, characters will die. Grin lends itself to deadly games and rally shines with 4-6 players and narrative arcs lasting 3-4 hours.
Pro Easy to improvise
With the intrinsic arc of a classic horror narrative built into the core mechanic, Grin can be an intuitive framework for improvised play.
Pro Unique mechanic
In true horror movie style, death becomes increasingly likely as the game's story moves irrevocably forward.
Pro Easy to pick up
The game has just one page of rules. It can be explained in a minute -- even to people who have no rpg experience.
Cons
Con Complicated magic system
Con Can be seen as too simple for some
Because each encounter has just two possible outcomes - success or death - there's little wiggle room in terms of roleplaying.