ProcessRenicer is a freeware program that lets you adjust the priority of different programs.
ProcessRenicer is a fantastic new tool of resource tweaking on OS X. It can be used, for example, if you have a single program (say a video encoder like Handbrake) that is taking up too much processor power. You can lower the application’s processing priority so it will allocate less resources. This will make the process take longer, but allows you to run other programs more efficiently in the background.
To change priorities in ProcessRenicer, you simply select a program and click “Renice Process”. This will let you change the “nice value” of the program.
The “nice value” actually seems to work value backwards. If you give a program a higher nice value, then it will have a lower priority. While a lower nice value means it has a higher priority. As long as you remember that this is a nice value it should be fine.
While this program does provide useful utilities, many programs do their own resource adjustment. Additionally, Mac OSX has its own little internal resource adjustment, but this program is great for small tweaks here and there. Just remember: always be careful about what you are changing.
You can download ProcessRenice here.