A question about transitioning players to GM-less gaming already exists (and it's a good one). I, however, am looking for a more exhaustive description (thus CW) of approaches to GM-less gaming. As such, I'll describe the traditional effects associated with the GM role, and answerers can help out describe how gaps that arise from the removal of the GM role can be filled.
Note: the GM is not automatically the host of the session: I'm going to ignore location / snacks / agenda's, etc.
Traditional elements of the GM role:
- Cohesive story (generation)
- Appropriate threat / challenge levels, both strategically and tactically
- Neutral arbiter of inter-player dispute
- NPC acting
- Story / scene pacing
- social cohesion / group makeup selection / spotlight distribution (this one may fall outside scope, but is often associated, I think)
If I missed antyhing, please let me know in the comments and I'll edit the question!