The core of the engine seems to be Unreal/Unreal 2 with loads of custom tech layered on top. There's this screen capture of the level editor:
![Image](https://i.imgur.com/AMmTy7M.jpg)
The .u files found in the MegaPackage can be found here: https://www.dropbox.com/s/0t5bee559qcc3 ... es.7z?dl=1
For the long story: Gearbox Software refused to release mod tools at release, they locked down the command console after release claiming people could use it to cheat in multiplayer (lol) - but most commands can be binded to keys and still function - an offer was made by Fred Schreiber (3DR VP) to prepare/release tools for free last year but Randy Pitchford didn't take him up on the offer saying there would be 'certification costs'.