Steam has exceeded the number of 6000 games in its digital store. That is almost double the figure of a year ago, when Valve announced that Steam was offering more than 3,700 titles. Almost all games are certainly available for Windows.
Anyone who is using the browse function of the Steam Store and look at all the games, will see that the counter is currently at 6256 games. For Windows filter the counter is on 6254. In total two games are available for OS X or Linux, but not Windows. 1448 games are available for Linux and 2243 games for OSX. The numbers do not include games that are no longer offered, but can still get into the libraries of players. By comparison, Origin has just over 500 games, and GOG just above 1200.
According to SteamDB, there are at least seven players who have more than 6000 games in their library. The number one ranking player has 6768 games and its account represents a value of $70,398 or 62,403 euros.
When Valve had 3700 games in September last year, the platform had 100 million users. How many there are now, is not known, but in February Valve reported having 125 million users. It is unclear what proportion of those users is actually active.