I've been using MO (oldrim) and NMM (TW3) for a few years now and have come to appreciate both. I've also studied Comp.Sci. and modded a few games for fun, so I do know my arse from my elbow when it comes to programming, even though I'm not employed as a software developer. @Tannin42: One thing that struck me when thinking about the vfs (imaginary filesystem from the game .exe's point of view) vs. virtualization (hard/symbolic links instead of files), is that maybe the overall best approach is actually to adopt something akin to what Plan 9 out of Bell Labs did: Turn the problem on its head and think of the original game as a 'file store' or 'source' instead of as a 'target', and link files from said 'file store' into a new, unique 'profile', which acts as a 'world view' and can 'bind' files from both the 'file store' and the various 'mod stores'. This allows you to keep the original install location *completely pristine* like MO does, yet still reap the benefits provided by symbolic/hard links like NMM 0.6x does. The only thing you might need here is some registry magic, where you trick the game .exe into believing you when you tell it that the game is installed in the 'profile' location. But since every game accesses the registry through a similar Windows API, this *might* not be such a big deal? == EXAMPLE This outlines the case where we have a single game profile configuration called 'my_profile' (there could be an arbitray number of these): - Game was originally installed to D:\Steam\SteamApps\common\Fallout 4 <- %FILE_STORE% (shared between profiles) - Mod archives are downloaded to D:\Vortex\FO4\downloads\ <- %MOD_DOWNLOAD_DIR% (shared between profiles) - Mod archives are unpacked to subfolders under D:\Vortex\FO4\unpacked\ <- %MOD_STORE% (shared between profiles) - Mod profiles live in subfolders under D:\Vortex\FO4\profiles\ <- %GAME_PROFILE_DIR% (each profile is unique) Now, each mod profile would be initialized with hardlinks of every single original game file (assuming that hardlinks are indistinguishable from the original files) placed into the %GAME_PROFILE_DIR%\my_profile\ folder. After that, Vortex would populate the %GAME_PROFILE_DIR%\my_profile\ folder with symbolic links from the %MOD_STORE% folder according to the user's vishes per GUI checkboxes and whatnot, making it easy to distinquish between which files are from the %FILE_STORE% and which are from the %MOD_STORE%. You could potentially allow 'normal' override files as well. When a modder develops his mod, he creates a 'my_mod_environment' profile and then creates his mod as %MOD_STORE%\my_mod and asks Vortex to add it to his %GAME_PROFILE_DIR%\my_mod_environment\ folder. Each time he makes a change in %MOD_STORE%\my_mod, he asks Vortex to re-populate %GAME_PROFILE_DIR%\my_mod_environment (this is the DevOps way -- you reset state every time you deploy for consistency's sake) and does the rinse-repeat dance until he's satisfied that he can cut a release of my_mod. This way, both the user and the developer get the freedom they need and absolutely NOTHING is changed in the original install location. END EXAMPLE == Thoughts?