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.
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.