Pandora getting too easy for you? Use the 4-player difficulty tool to trick the game into thinking there are more players in it. Requires the .NET Framework 4.0!!! This tool was created using NOPeR's research with Cheat Engine. It uses a simple memory hack to change the number of players Borderlands sees.
Q: Can I do this on my XBox or PS3?
A: No, this is for PC only
Q: Can I raise this to have more players than 4?
A: You can do it, but more than 4 players makes you invincible for some reason, so it defeats the purpose of the tool. This is true for both BL1 and 2.
Q: Do I need two different versions of the tool if I want to use them on both Borderlands 1 and 2?
A: No. The tool will detect whether you're playing Borderlands 1 or Borderlands 2 and do the right thing accordingly.
Q: Will I get banned for using this?
A: No. But note that this tool is a memory hack. As such, don't do anything foolish like keeping it open while playing games that use anti-cheat software like Team Fortress 2. Those programs work like virus scanners and it is theoretically possible they would notice that this program searches and changes memory and detect it as a cheat. However, BL1/BL2 don't use VAC or any other anti-cheat software so it's safe to use in those games.