As always if anyone needs educational help learning about steam emulators like the Goldberg Emulator or the SteamStub DRM remover (Steamless) just let me know/tag me!
Don't forget to check the emulation mega thread for other educational resources about how to play your legally acquired backups too.
Why run either Goldberg or SteamStub? Is it so I can download my friend's library or backups and use them myself? Can you play online with them with friends? Idk if I'm really interested but I am curious.
Goldberg emulator is a Steam (steam_api.dll in practice) emulator that allows you to play any game backups that don't have SteamStub (or other) DRM on them. Steamless is for removing SteamStub DRM from game executables (not all steam games have these) where you can then apply the Goldberg steam_api.dll replacement onto to allow you to play those backups.
Certain games (likely any game that has direct-connect features where you punch in an IP address) will be playable with friends online. Some games that use traditional matchmaking can utilize the matchmaking services of other steam games (through making steam think that it's matchmaking for game ABC when it's actually doing it for XYZ) and allow people with backup copies to play together through "official" steam matchmaking services.