Edit: RISS has moved!
For older, historical, once-official entries into the RISS canon, read on. This is still the place for discussion of RISS!This is version 1.3 of what used to be called GDNS official, canonical theory and is now renamed RISS official, canonical theory.
Because getting on the same page about which techniques are kosher and which are iffy is SUPER IMPORTANT to us humans! It's the outside-in approach to finding common value ground!
Now what is RISS? It stands for Rails, Impro, Sandbox and Spike!
In Rails, one or more of the participants is a super talented story writer in the attic and pre-writes a very interesting story that the group can then bring to life and experience in full color at the gaming table! This could be a GM writing "First the players are gonna do X, then they're gonna do Y, then they're gonna do Z" style notes before play, this could be a player writing ten pages of backstory for their character which is going to be recounted closely during play!
In Impro, one or more of the participants is a hippie! They want to encounter choices that would be meaningful diegetically, such as "Should the hard-working cop abandon her family in order to protect them?". The most important life dream of a Impro hippie is that a very unexpected story is created during play that can then be retold to your hippie friends at the next con!
In Spike, one or more of the participants is a power-hungry munchkin! They want to encounter choices that would be meaningful mechanically, such as "Should the hard-working cop equip a +1 one beastmaster sword or a x3 mod lightning round gun in order to best protect her family?". The most important life dream of a Spike munchkin is to test their own might! To face challenges and bravely stare them down with their lifelong journey of system mastery!
In Sandbox, one or more of the participants is a curious individual! They want to examine the clockwork of the system, how will the little ants in the sandhill move around and what will happen when they collide! The most important life dream of a curious and imaginative Sandbox daydreamer is to see their doll's house come to life and see the dolls do What They Would've Done Really. If they were alive. But with spaceships.
Wait, there's more!
These four corners of the RISS quartet may sound like mortal enemies. But that's not the case, they are the best of friends!
Here is the official poster for the RISS kumbaya of FRIENDSHIP:
But not everything is a paradise in the RISS land!
Here is the official diagram of the official RISS Hatred Parade of Eternal Enmity: