Don’t worry, in S&box, Facepunch’s other game, they will completely rid of this system, they too thought it was stupid to force someone to buy other games just to enjoy addons made by other people.
It’s the Steam Console Client, basically, it allows you to do various things related to the steam servers, like upload addons to the workshop or manually download updates / content for games, normally to do so you need to own the game, but CS:S is one of the games valve allows you to download the game’s content without actually owning the game. https://developer.valvesoftware.com/wiki/SteamCMD
There are guides on how to download CS:S content for free.
Wow, so this is only really good for Gmod and for if you’re a source map maker, right? Because you don’t get the game, you still have to buy it to play it, but you get the weapons and models and textures and shit. Am I correct?
I’m not sure if legally you’re allowed to use them in your own projects, but definitely for content meant for Gmod, since they have a license for the whole game mounting stuff.
It is the literal official steam console, it is antiquated but steam and its console are one of the same, just different looks, Facepunch also endorses downloading the content from the CMD, it’s one of the pinned messages in the gmod server.