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Copyright © 2023 Robin Scott. All rights reserved.
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Copyright © 2023 Robin Scott. All rights reserved.

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Tannin - MO2 Team

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LePresidente

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About this mod

Mod Organizer (MO) is a tool for managing mod collections of arbitrary size. It is specifically designed for people who like to experiment with mods and thus need an easy and reliable way to install and uninstall them.

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(video by DarkPopulous)



Mod Organizer 2 is a mod manager created by Tannin to support 64bit games like Skyrim Special Edition and Fallout 4 in addition to all the 32bit games MO1 already supported.
Tannin discontinued the project when he was hired by the Nexus team to develop their new Vortex mod manager.
MO2 was not completed and was left with many issues. LePresidente managed to fix it to a usable state by himself after SkyrimSE came out, adding support for it, and releasing v2.0.8.
The project took up speed again after a few more coders showed up in late 2017, and an incredible amount of work has been done!

Credits to Tannin, LePresidente, Silarn, erasmux, AL12, LostDragonist, isa, AnyOldName3, Holt59 and many others for the development.

A Special Thanks to all the testers of the discord server and everyone else involved for supporting the project!

MO2 Team:
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Mod Organizer v2.4.1 has been released, see the logs section for all the changes.
Mod Organizer 2 Full Changelog [github.com]

Attention! The new version requires the newest Visual C++ 2019 redists installed: https://aka.ms/vs/16/release/vc_redist.x64.exe
Attention! The new version requires .NET Framework 4.8 installed: https://dotnet.microsoft.com/download/dotnet-framework/thank-you/net48-web-installer

Mod organizer 1 Legacy (thanks enpinion):
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Mod Organizer 2 is an open project in the hands of the community, there are problems that need to be solved and things that could be added. MO2 really needs developers and if you have the programming skills and some free time you can really improve the experience of the modding community.
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Short Version:

Mod Organizer 2 (MO2) is a feature rich Mod Manager.
MO2 is very advanced and specialized for Bethesda games. Here is the list of supported titles:

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What distinguishes MO2 from more traditional mod managers is the idea of not modifying the "vanilla" game installation in any way. Mods are not actually installed in the game folder but instead are kept each in their own separate folders. The game INI configuration files are not touched and instead MO2 uses it's own set.
This way mods are only "active" if the game is started from MO2, while if it's started normally it will be in it's "vanilla" unmodded state.

What this means for users is that enabling/disabling mods doesn't actually require any file transfers, it can be done instantly. The order in which mods are "installed" can also be modified at any moment with drag & drop, easily changing which mods are winning file conflicts.

Users can change the entire setup with a couple of click by using different Profiles of enabled mods. Each profile has it's own order of mods and plugins and even it's own set of INI files, different from the ones in MyGames which are left untouched.

Users should change INI settings from within MO2 by using the integrated INI Editor. If they need some other program to also see the installed mods, they can add it to the list of executables and start it from MO2, so that the mods may be shown.

Long Version:

Mod Organizer (MO) is a tool for managing mod collections of arbitrary size. It is specifically designed for people who like to experiment with mods and thus need an easy and reliable way to install and uninstall them.

The special fact about MO2 is that it uses a Virtual File System (VFS) instead of actually installing your mods into the Data folder of the game.
MO2 uses it's VFS to trick the game and other programs into thinking that the mods are installed in the data folder while they are actually installed in their own separated folders. This VFS is called USVFS (User Space VFS), which is different from the VFS that MO1 used, since the old one did not support 64bit programs, but it works on a similar concept.
Which means that only programs started through MO2 will see the mods, while for the rest of the world the game will remain vanilla.

The VFS works by hooking the target program (and any of it's children processes), intercepting all the requests of accessing files and folders, if those are referred to the game Data folder then usvfs will intervene and change the answer so that it looks to the program like all the Mods files are located there as well (this kind of behavior is similar to how some types of malware behave and that is why some Antivirus will flag usvfs badly).
This system allows for a process specific virtual folder that does not take up space and can be interacted with without having to actually move or copy any files.

The implementation of usvfs is quite complex and low level as it goes and hooks Windows API calls, keeping a shared record across hooked process of the changes such as added files and deleted ones in real time.
Usvfs is a standalone library that is meant to be usable in different applications other than MO2, as such it does not contain MO specific code like the MO1 VFS did (hook.dll).

Differences with Mod Organizer 1:

MO1 and Mo2 can be considered different programs. The main difference between the two is that the virtual file system (vfs) used by Mo1 does did not support 64bit games. Because of this MO2 has a completely new vfs library (called usvfs) that was made to support 64bit programs as well. This library is more separate and independent from the rest of the program allowing for it to be potentially used even by other programs.

Another major difference is that Mo1 had a special system to manage Bethesda Archives (BSAs). 
Tannin (the creator of both MO1 and MO2) decided to not include this feature in MO2 for the fact that it subverted how the the game actually loaded the Archives causing problems with tools and mods that relied on the original system to work. That in addition to the sheer complexity of implementing the feature with the new virtualization library and making it work with all the supported games (the Mo1 system was based on a hack).
From his experience and all the problems he had with Mo1, Tannin came to the conclusion that using a special system for BSA management that did not follow what the game did was a mistake.
We agree on that fact, having seen the problems it caused and compromises that the feature would have required. 

We are working though in restoring BSA (and all other typs of Archives like BA2) parsing for conflict detection. This time it will follow the standard game rules, which are:
All Archives are loaded in the order of the plugins loading them (in Mo2 you can't disable dummy plugins), and after that all loose assets are loaded on top. So loose assets can't be overwritten by archives.
We are looking for the best ways to visually show the conflicts of BSAs as they don't follow left pane order anymore, but right pane instead.
We will be looking into ways to not use dummy plugins to load BSAs in the future.

MO2 is of course receiving active development from the community while Mo1 does not, which means that there are and will be new features in MO2.
Listing everything here would be too long so to have a better idea of all the things that Mo2 adds you are invited to read the Changelogs that you can find under the LOGS tab.

Here is the list of all the games currently supported by MO2:

  •  Morrowind
  •  Oblivion(*)
  •  Fallout 3
  •  Fallout NV
  •  Tale of Two Wastelands (TTW)
  •  Skyrim
  •  Skyrim SE
  •  Skyrim VR 
  •  Fallout 4
  •  Fallout 4 VR
  •  Enderal (Steam Edition)
(*)To use OBSE with Mo2 you need to follow these steps [github.com]as otherwise you can't load it.



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Mod Organizer 2 supports third party plugins!
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Mo2 is a 64bit application and as such it requires a 64bit operating system to run.
Mod Organizer 2 works with the vast majority of tools. What this means is that they can be made to work on the "virtual" data tree.
Among the tested applications are: OBMM (though OMOD scripts may not compile properly), FOMM, MLOX, LOOT, Wrye Bash, FNIS, xEdit, DynDOLOD... and many more.

If you find an application that does not work, please report it to us.



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Issues, problems and suggestions should be reported to the open discord server: ModOrganizerDevs [discord.gg] or to the github page (in case they are not user specific): Github issues page [github.com].
Discord is also where dev builds are tested, bugs are reported and investigated, suggestions are discussed etc. There is a good number of users there willing to help people with issues in addition to the Developers, so that they don't have to handle everything personally.
Please don't post issues in the comment section, as monitoring them would be highly inefficient and inconvenient for the developers. Discord and GitHub offer much better and efficient ways to keep track of issues and debug directly with the users that have the problem.


Here are some of the themes and splash screens you can use to customize the look and feel of Mod Organizer 2:
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If you would like your theme/stylesheet/splashscreen to be added to the list contact us on the MO2 Dev discord.