Steam
Steam is a digital marketplace by Valve that primarily is used to sell video games. However it also sells various programs, too!
Usage
Steam isn't really related to tennis other than being a marketplace for various tools. However, you may need it installed for certain programs that tie into its copyright protection measures.
Available Programs
SteamOS
SteamOS is an Arch Linux based operating system made specifically to run on the Steam Deck; Steam's flagship portable console. As it uses Linux and not Windows (which is common for most video games), it uses the Proton layer to emulate many of the system calls and libraries common in Windows programs.