DBoost for Mac

From Malibutu Software:

DBoost is a Mac OS X utility which redistributes CPU time to give the frontmost application about 20% to 30% more processor time than it get's normally. It uses the UNIX command "renice" to change the priority of the frontmost application so that the processor gives it more time. You can also manually set the priority of all applications via the "Status" window, where you also can force quit and check the priority of applications and processes.