Works on Mavericks just fine. Just have to fully uninstall and reinstall everything, as usual. Mine is a mid-2009 MBP, and I definitey rely on Coolbook. Keeps me at least 20C cooler, and extends my battery by 25% ish.... Awesome. Note that Coolbook reportedly Does NOT work on i5 and newer Intel Mac Machines. Just us special Core 2 Duo Peeps, and earlier. I also hear it works on iMacs and Mac Pros, with these earlier processors. For those having issues or needing details, they are below. This processes addresses all the hiccups I have encountered in my 4 years of using Coolbook. Annoying, but hey, great benefit with no useful alternatives, and yes Coolbook is well worth the $10 in my opinion. 0. If you have never had Coolbook installed, first goto www.coolbook.se and see if it even works for your machine. If it will, great! You can go straight to step 7. Upgraders should first... 1. BEFORE updating OSx, ever, delete SleepEnabler.kext from System/Library/Extensions 2. Empty Trash 3. Reinstall AppleIntelCPUPowerManagement.kext and AppleIntelCPUPowerManagementClient.kext (hopefully you saved them Like I have learned to)(I use Kext Helper B7) 4. Open Coolbook and do two things - Take screen shots of your current settings for future reference - Open preferences, and Uninstall 5. Restart 6. Upgrade your OSx. Without steps 1-5, my upgrades typically failed, or I enjoyed kernel panics. Your mileage may vary. If you accidentally upgraded first, and your MB works, then simply skip step 3 above, and you will hopefully avoid kernel panics. Once OSx is updated to Lion (10.7.x), Mountain Lion(10.8.x), or Mavericks (10.9.x)... 7. Copy the files you will need now and for future OSx upgrades into a folder you can find again: - Coolbook.dmg (v2.22 is current) from www.coolbook.se - Sleepenabler.kext from code.google.com/p/xnu-sleep-enabler/ (10.7-8 is current, & works for 10.9) - Kext Helper B7, or other kext install utility - In System/Library/Extensions, copy the following two files: (Note that Alt-Go menu takes you to root Library instead of System/Library, where 'Extensions' resides) + AppleIntelCPUPowerManagement.kext + AppleIntelCPUPowerManagementClient.kext - The screen shots you got earlier of your cookbook settings - A web link to this page in case you need another walkthrough. ;-) 8.Delete the two AppleIntelCPUPowerManagement kexts from that Extensions folder 9. Install the SleepEnabler Kext (again, I use Kext Helper B7) 10. Restart 11. Open Coolbook.dmg, and install 12. Open Coolbook. (Note it is not signed for Mavericks and You will Need to Control-click the application, then select Open on the first time) 13. It should ask if you want to install, you will say yes, and have to reboot (sigh) 14. Open Coolbook, Add your password and registration settings 15a. If you have your voltage settings, you can just enter them and save without testing. If they worked before, they should still work now. 15b. If you do not have your voltage settings, you'll have to find another reference for that whole process. 15. Restart and done For some reason, it seems the program has to be open on my machine in order for the settings to actually work. I always restart while selecting "open programs on restart", then just press Alt-H to hide cookbook when it comes up, if it comes up. To monitor that it is working, go to preferences and select menu display. You can then click the menu in the top bar and select all options except 'hide menu'. Good luck!