Also, I've personally tested this method with PCs that were freshly built and completely offline, not even connected to a local network, just to make sure that everything worked flawlessly.
I'll be outlining how to do this in Windows, but the process should be exactly the same on Mac and Linux (I've been doing this in both Windows and Linux without any issues). The method I'm showing you to keep Steam offline forever is built into the client itself. Keep in mind that NOTHING I'm doing here is illegal or against Valve's rules I am using Steam 100% the way it's meant to be used, with no outside software or hacks/cracks of any kind. There are some exceptions, which I'll explain after going through the main walkthrough of how to do this, but the vast majority of Steam games will actually allow it to happen.
Using Steam's Offline Mode, it's actually possible to play your Steam games offline forever, no matter what PC you're using, and transfer them from machine to machine without ever needing to go online to activate, verify, validate, or ask permission to play the games you've purchased. In fact, if a game isn't listed on the wiki, then it most likely falls into this Steam-required category, meaning that if Steam goes down, you won't be able to access your games. But most Steam games do, at the very least, require the client to be running and the user to be logged into an account. For a lot of games, that's actually okay the GOG community thread here ( ) and the GOG community-maintained wiki page here ( ) has a list of Steam games that are actually DRM-free, games that only absolutely require Steam as a delivery service and nothing more. I think everyone here will agree that DRM-free games are better than being restricted by online-dependent measures, but it's also hard to deny the fact that if you want to play most triple-A games on the PC, you're going to have to go through Steam.