Valve along with their partners at open source consulting firm Collabora have ported over the standalone Steam Link application to the traditional Linux desktop.
Originally available as the Steam Link hardware that was discontinued in 2018, which Valve then replaced with the standalone application. The idea is that it allows you to stream content from Steam on one PC to another, or to a different device like an Android phone. Previously the app was only supported for Windows, iOS, Android, or a Raspberry Pi but that ends now with the official announcement today adding traditional Linux desktops to the mix.
So why now? Well, Valve only just recently announced Remote Play Together - Invite Anyone, which uses the Steam Link to allow people without a Steam account to join a game hosted by someone else. So you could host a game of your favourite co-op or multiplayer experience, let's say Stardew Valley, and someone only needs the Steam Link installed on whatever device they have available to join your game with a link you send over.