TIL Rockstar has its own games launcher too. It has a whopping 7 games on it, which is kind of pathetic. Whatever though, free is free. So anyone interested, today, for you:
The PC version of Grand Theft Auto San Andreas will be free for a limited time on the Rockstar Games Launcher. You need to download the client, install it, log into your Rockstar Social Club account (assuming you have one), then go to the in-client store to San Andreas' page, then click the "Claim free game" button.
Have a look if interested and enjoy.