The patcher doesn't include any copyrighted files so you'll need a legitimate copy of Fallout 3 to use it, and it should not be used to install Tale of Two Wastelands 3.2-use this downgrader instead.

Once it's installed you can boot the game however you like-through Steam or GOG, the launcher, or any mod manager-but if you want FOSE to auto-load you'll need to do it with the Fallout3.exe directly, so you'll probably want to create a shortcut. The patch will work with both the standard and Game of the Year editions of Fallout 3 on Steam or GOG. It also automatically loads FOSE when Fallout 3 is started (if it's installed) and enables the game to use 4GB of RAM: Some older Bethesda games, including Fallout 3, have a 2GB limit on RAM usage, and patching that up to 4GB can have a very positive impact on performance.

Enter the Fallout Anniversary Patcher, by mod maker lStewieAl, which restores FOSE functionality by downgrading Fallout 3 to the pre-update version 1.7.0.3, while maintaining the removal of Games for Windows Live dependences.

Fallout mod manager crash