What is the Universal Rating System (URS)?

The Universal Rating System is an alternate rating system which, according to the project's web site:

The Universal Rating System™ (URS™ for short), is a revolutionary new sport’s rating system designed to assess the relative strength of participants across a wide variety of competitor vs competitor sports or games.

The URS™ was developed as the result of a collaborative research project funded by the Grand Chess Tour, the Kasparov Chess Foundation and the Chess Club and Scholastic Center of Saint Louis.

According to the project's FAQ page, the major differences between URS ratings and FIDE Elo ratings are:

There are many differences between the URS™ and the FIDE system. The most striking difference is that the URS™ calculates only one rating for each player, informed by their results at all rates of play. This published rating is the URS™ system's assessment of each player's strength at Classical chess (defined as a rate of play where each player has at least 2 hours for their first 60 moves). The URS™ recognizes that there is useful information about a player's over-the-board chess strength in all game results regardless of the time limit, and can therefore more effectively estimate a player's Classical chess strength by also considering their results at games played at faster time controls. As the speed of play increases, the URS™ assigns less and less importance to the game results relative to games played at slower time controls.

Furthermore, the URS™ is a weighted performance rating, calculated across several years of previous game results for all players. Older games are given less importance than more recent games, by applying an exponential decay rate. Unlike traditional performance ratings, which are based upon the opponents' rating at the time the game was played, the URS™ constantly reassesses the strength of all opponents and searches for the most likely set of current ratings for all players, in order to best explain the observed results.