SPOKEN  Coolbook made my first generation Macbook Air usable! I was running WinXP under VMWare, and before CoolBook, this configuration came crawling to an overheating near standstill... I had concluded that the Air was pretty much unusable for my needs.

After installing and configuring Coolbook, the Air performs very well in this configuration - and amazingly, the processor seems to thrive on the minimum settable voltage at every possible clock speed.

$10 saved my MacBook Air. So what if it's locked to a specific computer? It's $10. Buy it again for the next laptop.  
(Version 2.15)

TRONDAH  Does not work in latest Snow Leopard seed. Kext does not load in 64 bit mode. It loads in 32 bit but kextcache parameters changed, complains about wrong arguments in the logs.  
(Version 2.14)

BLULOO  Buy new hardware? Want to reinstall your registered coolbook app?

The developer will tell you you're out of luck.

Neat little app but the dev says registration is only good for a specific machine.

You have to pony up more $$ for another license.

Lame policy for an otherwise useful app.  
(Version 2.14)

MHOLLIDAY84  My Macbook Air would always get really hot, and the video would start skipping when watching shows on ABC.com. With Coolbook, I was able to reduce the temperature of the core so that it wouldn't shut down and mess up my stories. used 0.9 V for all except 1600 MHz, for which I used 0.95 V. This software did exactly what it was supposed to.

I have a feeling that the reason some others didn't get as good of results as I did, is that they either don't know how to use the software, or they don't have their laptop on a flat surface. Remember that temperature transfers fastest from solid to solid vs. solid to air. My in-table for instance acts as a heat sync.  
(Version 2.14)

PEN_SQ  The 2.13 update is severely broken on my 2007 white MacBook (with i950). The first hint is when it is required to redo registration. After that, my voltage settings were lost. After rediscovering and entering the voltages, I didn't see Coolbook do anything useful with them.

I uninstalled and went back to version 2.12.   
(Version 2.13)

MICKFISH  I've been using CoolBook for a couple of weeks & I'm very happy with it. Straightforward & clearly explained. Did exactly what it said it would with the minimum of fuss & effort - what more could you want? Worth the money? Definitely. Can't really answer for stability but I'm pretty confident judging by results so far.  
(Version 2.12)

SAMPLER  CoolBook does much more than fan control. It can be used to decrease voltage, at no cost to processor speed, and thus it can reduce power consumption and heat. It looks like a must for the new MacBooks. See:

http://www.edn.com/blog/400000040/post/1890037389.html  
(Version 2.10)

HYBSTER  You should be aware that the author of the program insists on a strict "one machine" license, you will only be able to use this with one computer. If you upgrade, you will have to pay again. Stupid policy? Up to you...

"The license is for one computer only."

-Magnus Lundholm  
(Version 2.9)

HYBSTER  You should be aware that the author of the program insists on a strict "one machine" license, you will only be able to use this with one computer. If you upgrade, you will have to pay again. Stupid policy? Up to you...

"The license is for one computer only."

-Magnus Lundholm  
(Version 2.9)

DRDUL  Great app! Installed this on my Mac mini (FWIW, my settings are 1670 MHz/0.95 V and 2004 MHz/1.00 V). Temperatures used to hit 70 degrees Celsius for no apparent reason, and now remain in the mid-40s.  
(Version 2.9)

JKAHAN  Excellent product. I just installed it on my Macbook Air and no longer have heat or core shutdowns. Search the posts on macrumors for "underclock" and there is a good thread comparing everyone's coolbook settings.

The GUI could use some work though....  
(Version 2.8)

THANAR  Looks like Coolbook throttling is broken under newest Mac OS X 10.5.2, although it used to work fine under 10.5.1.  
(Version 2.6)

JETFIREDX  Wouldn't install the driver on Leopard. I have the last version of the controller on the system from upgrading with migration assistant, but the last driver is not there since I formatted and started a clean install.  
(Version 2.5)

TOMASX  This app is well worth the tiny price. I have used it for almost a year now with a 17" Macbook pro (core 2 duo). The default settings left it running fairly hot, but after spending 20 minutes figuring out the minimum voltages needed per frequency I had some settings that have been totally stable.

When you're on battery you get much better performance and use less energy, by setting the voltage to the minimum but the frequency to the max that voltage can power (for me this was almost double the CPUs normal minimum).

and for desktop work you can use the max CPU speed with a big cut in power, meaning less heat and nose from fans.

In case it helps someone out, my settings turned out to be; 1837MHz-0.95V, 2004Mhz-0.9625V, 2171Mhz-1V, 2338Mhz-1.05V.  
(Version 2.3)

PAULVICTOLY  I purchased this today after I was informed by the developer that the latest version supported Santa Rosa based MBPs. My settings ended up being 0.85v for 1200mhz, 0.90v for 1600mhz, 0.925v for 2000mhz, and 1.0625v for 2400mhz. Not too bad!  
(Version 2.3)

JETFIREDX  Just registered today after reading the good reviews and wanting my MacBook to run cooler. Working well with my first level of undervolting. For $10 it seems to be well worth giving a shot. A few small suggestions: Would it be possible to have the ability to remove a single Frequency / Voltage pair from the lists? As it is, if you add the wrong values you have the clear the entire list and add them all again...a bit of a pain and I did this several times today messing with the settings. Second, tying in the ability to control the fan speed would be handy too. I always thought the fans kicked up too slowly on my MacBook, letting the heat build up more than it needed to. Having an option of setting minimum fan RPM per frequency would be nice because when I am running at full speed the fans could go faster before the temperature would normally tell them to kick up.   
(Version 2.3)

ERIC PETIT  Worth the $10

I have been using it for several months, my MBP CoreDuo 2Ghz is stable with the minimal voltage (0.95V) at 1000-1670Mhz, 0.9875V at 1837Mhz and 1.0625V at 2000Mhz - which makes it sensibly cooler.

Coolbook is also essential if, like me, you often use your MBP without the battery : Apple's defaults then limit the CPU at 1Ghz, while Coolbook will let you use any frequency.

One small feature request: I usually let it throttle within 1000-1670Mhz when I am on battery, except when I really need the longest battery life (like on the train) and keep the CPU at 1Ghz. It would be handy to be able to define presets so that I can easily switch between those two settings.  
(Version 2.2)

BOB_TM  I upgraded my Mac Mini 1.5GHz Core Solo to a 2GHz Core 2 Duo (T7200) and the CPU got quite hot (reaching 87-88+ C during 100% load on both cores) and activated the fan control mechanism causing more fan noise. After installing this utility I managed to get a stable voltage of 1.0126V and reduced this maximum to around 75 C and the fan speed remained on the default value throughout my testing.

On the downside, the program GUI needs some work to be intuitive (at least for me) and the documentation improved. Fan speed information (maybe even load information on each core) and title bar display would give this gem a 5 star across the board.

I recommend this highly for anyone with Core 2 Duo on the Mac Mini and would guess that it would be of value to any Mac Mini user who wants little fan noise.  
(Version 2.0)

SOSA11  On my Win laptop i used RMClock and found it very useful. I am glad that somebody makes an effort to migrate it to mac.

I was especially looking for the dinamic clocking-undervolting feature and glad that the developer (Magnus) succeed to implement it. I am using for a week now and my MBP runs cooler and longer on batteries without performance sacrifice.

Very useful little tool!  
(Version 1.1)

MACBPUSER  I've been using coolbook for one month, and I'm very pleased with it.

At first I did not know how to setup the program for the best effect, I just locked the CPU at the lowest frequency. This made the computer run cooler and I got more battery time.

Then I talked to the developer of coolbook, and he suggested setting the highest stable frequency for the lowest voltage. For my macbook this is 1.67Ghz at 0.95v. This is one step from the highest frequency setting at the lowest voltage setting!

1.83Ghz 1.2625v is the highest stock setting for my macbook. I now run it locked at 1.6Ghz 0.95v for battery and 1.83Ghz 0.9875v for AC. This keeps my macbook cool and quiet.

I know there is a beta version of coolbook that allows dynamic switching, but I have not tested that one. I'm happy with my setup.

I have not had any problems with stability.

The value of this product is great, the added battery life alone is worth more than $10 for me.

The support is very good. The author replies very fast.  
(Version 1.1)

DELARUE  This is not shareware as it is not possible to use the programs functionality before buying a license. Without registering, all controls are disabled and only the current CPU frequency, voltage and temperature are shown.  
(Version 1.1)

UNDERVOLTER  Finally! I have been looking for a app like this. I used to undervolt my notebooks in windows to reduce power consumption, and have missed this type of app in OS X.  
(Version 1.0)