Do alternatives to Elo exist for non-team/individual events? Are there any well-known rating or ranking systems, similar to Elo, for multi-participant events? For example, a system that can rate various forms of racing (auto, downhill, horse etc.) or other individual sports (golf, for example)?
 A: It seems that rankade, our ranking system for sports, games, and more, fits your needs. It's free to use and it's designed to manage rankings for small or large groups of players. It can manage any kind of match: one-on-one, faction vs. faction (two teams, which may be asymmetrical),
multiplayer, multi-faction, cooperative games, single player games, and so on.
Here's a comparison between most known ranking systems, including Elo, Glicko and Trueskill.
A: Yes- there are many versions of multi-participant rating systems, many of which are modified versions of the base Elo system (one of Elo's great strengths is that it can be readily modified).
One very interesting multi-participant ranking system is Microsoft's TrueSkill Ranking system based on bayesian inference of player skill. The rating is used in matchmaking and ranking of many of their online offerings. Quite a lot of other research has been done on the system. (Full disclosure: no professional relationship with Microsoft)
More theoretical underpinnings and consequences of bayesian approximations as applied to rating systems can be found here, here, and here.
A: TravisVox, not sure if you are wanting to produce rankings of Horses, or Handicappers/Horseplayers.  I'm interested in both.
You probably already know all this, but:
BrisnetDOTcom produces statistics which rate the "Class" of the horses
that each horse in today's race has raced against in the past.
They also produce a "Power Ranking" comparing only the horses in the race with each other.
They also produce a rating which measures the highest level of competition against which a horse has performed well.
After all, any horse can enter a high level stakes race if the owner has more money than brains...but the benchmark is how well a horse can perform at higher levels of competition.
Regarding horseplayers, I am in the early stages of collecting stats on how to rank horseplayers who compete against each other in Tournaments.
Would love to collaborate, or touch base.
