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)?
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.