MechVM started out as a reverse engineering effort for the computer games MechWarrior 2: 31st Century Combat, MechWarrior 2: Ghost Bear's Legacy and MechWarrior 2: Mercenaries. Over time, additional features were added to install the different versions of the games. Eventually, it turned out that some editions of the game do not run well anymore under Windows editions past and including Windows 8, so the focus shifted towards recreating the game.
At this point, MechVM installs all known editions of MechWarrior 2 with available patches to make the game run as smoothly as possible. It also contains players for the sound, graphics and video formats used in the engine. In some editions of MechWarrior 2, the mech lab didn't work well, so a reimplementation of the mech lab was added. When it became clear that some editions of MechWarrior 2 did not work anymore in newer editions of Windows, a reimplementation of the entire game was started. That effort is currently ongoing. Currently, many missions can be played, but not all missions have been implemented. By installing MechWarrior 2: 31st Century Combat and MechWarrior 2: Ghost Bear's Legacy via MechVM, that preview is made available in the "Play Game" menu.
MechVM provides methods to play various editions of MechWarrior 2, as published by Activision. The canonicity of MechWarrior 2 is discussed in the games' pages. MechVM also incorporates code that allows to play the games without use of the original engine. In that case, efforts are made to bring the game a little more in line with current BattleTech canon. This is mostly done by exchanging Mechs that are considered rare for a faction to be used less often. On the whole, MechVM of course does not contribute to BattleTech canon, and that is not the intention either. The intent of MechVM is to allow users to experience BattleTech from the viewpoint of the 90ies games instead.
The file formats were discussed in the mech2.org forum, which was kept online for documentation purposes even though most of the discussion takes place on discord these days. MechVM is available as a Windows executable that includes source code.