OPULauncher is a convenience launcher for Outpost 2, that specifies enabling the Outpost Universe unofficial modifications. It can also check online for new OPU mod updates.
Aside from the update checker, OPULauncher is the equivalent of running Outpost2.exe /OPU. To run the game under a debugger, you may wish to do that instead of going through OPULauncher.exe in order to sidestep child process debugging issues.
OPULauncher does not itself inject the op2ext mod loader into Outpost 2; that is handled by the OPULoaderShim project.