Activity Monitor is a window to the innermost workings of your Mac. It monitors all of the running programs and processes, let you know where all your processing power and RAM is going, and provides enough useful information to diagnose many problems your Mac may be having.
But as useful as Activity Monitor is, there are many more monitoring apps made by third-party developers that can be of use to the discerning Mac user. Each has something to make it stand out from the rest.
Some are free, some are not. Here's the cream of the crop.
The Free Ones
MenuMeters
The first thing I should point out is that MenuMeters is not compatible with the El Capitan 10.11 Public Beta - and when it comes out of beta, the developers say MenuMeters may never be compatible.
To quote:
Due to new Apple-enforced code signature restrictions, MenuMeters is not compatible with the OS X 10.11 "El Capitan" public beta. Although the restriction is similar, this is not directly related to 10.11's "System Integrity Protection" (SIP, aka "rootless") feature and disabling SIP has no effect on MenuMeters.
Unless Apple makes the signature restriction optional, it is not clear that MenuMeters in its present form can ever be made compatible with OS X 10.11.
So MenuMeters is only suitable for those running Yosemite or older. I am including it in this list regardless, due to the high praise it is receiving from users everywhere and its wallet-friendly price point.
MenuMeters, as the name suggests, is an app which places a group of meters in your Mac menu bar. They can be customized to show whatever you want, and each element can be dragged into a different position to suit you. The monitor can quickly shows you CPU, Disk Activity, Memory, and Net activity at a glance.
XRG
This is one that I really like. Called XRG (X Resource Graph), it is a highly customizable dashboard, where you can see everything from the CPU usage to the weather. In fact I love it so much that it will now have permanent residency status on my desktop. And I don't allow any old app to live there, you know.
You can have it updating as fast as every 0.2 seconds, specify what you want to see and omit (so you don't get overloaded with information), and you can even specify the appearance of the widget. Oh and it's free!
Memory Clean [No Longer Available]
Memory Clean is focused solely on your Mac's memory usage. It was featured by Apple themselves last year as an "invaluable utility" during an App Store promotion, and Macworld declared it a "Mac Gem" back in 2013.
It only has one function — to optimize your Mac's memory by purging inactive memory. It is most effective after you have finished using a memory-intensive app or game (close Chrome and watch your memory amount surge). It also shows apps which are using significant memory, so you know which ones you should try to close to make your computer go a bit faster.
Activity Monitor serves a similar purpose under the Memory tab, but Memory Clean provides a prettier interface and fast menu bar access, which makes it worth a download in our opinion.
gfxCardStatus
This one only works if you have a MacBook Pro with dual GPUs, because these are the only users who would see any benefit.
According to developers, gfxCardStatus "allows MacBook Pro users to see which apps are affecting their battery life by using the more power-hungry graphics". So it's an app which tells you which graphics card your MacBook Pro is using (integrated "software" or discrete "hardware" acceleration). If you notice your Mac is using the "wrong" one, you can switch over to the one you want. This enables you to improve system performance and battery life.
In fact, Ars Technica claims that by using this, you can get as much as 8.5 hours of continuous use of your Mac, after some minor battery tweaks.
The Paid Ones
Now that we have taken a look at the best free ones, let's take a look at some paid ones. Obviously, being paid, these should be of slightly higher quality, though some of you may object to paying when there are four capable apps above.
Stater ($4.99)
I really like this one, and $4.99 is not that unreasonable. Stater sits in your dock as an icon and a menu. You just have to click the icon depending on what you want to see. You can choose from combined and multi-core CPU usage, memory usage, and drive space. You can switch off any that you don't need, and you even get six color schemes to match your desktop.
Monity ($2.99)
If you are a big Notification Center fan, then Monity will appeal to you, as it integrates excellently. After installing, just open Notification Center, click Edit at the bottom, and click the plus next to Monity. This should appeal to anyone who dislikes dock icons or items sitting in the menu bar.
As well as the usual activity stats (CPU, memory, disk), it also tells you how much battery power you have left, how much space is left on your hard drive, and what's going on in your network (such as your current internal and external IP, and incoming and outgoing traffic).
Temperature Gauge ($4.99)
Just like Memory Clean, Temperature Gauge has one purpose only — to provide every possible temperature your Mac has. It keeps tabs on every temperature sensor in your Mac and alerts you if something gets too hot. You can see how fast the fans are spinning, and all activity is logged to a .CSV file — handy for troubleshooting heat-related issues.
iStats Menus 5 ($18/$25)
Fair warning - iStats Menu is the most expensive of the bunch here, clocking in at $18 for a single license and $25 for a "family license". But everywhere I read, everyone had rave reviews for iStats Menu. They couldn't get enough of it. And it's not difficult to see why.
iStats has every conceivable stat about your Mac than you could hope to place on a chart. It digs down into the disk activity for every single app you have running to see which ones are the vampire apps sucking your Mac's blood (cough... Chrome... cough).
There are far too many features for me to possibly list them all here, so head on over to the iStats homepage to see what you get for your $18 if you absolutely must monitor everything.
System Monitor ($4.99)
System Monitor sits up in your menu bar (and takes up a lot of room by the looks of things), and gives you the usual computer activity. It provides useful stuff such as process load, CPU temperature, memory consumption, storage space, disk activity, and much more.
Happy Monitoring
This is just a small selection of the Activity Monitors on offer, but based on our exhaustive research these are the best of the lot. While there are not many free possibilities, the paid ones, with the exception of iStat Menus, are reasonably well-priced and within the budgets of most people.
So — is Activity Monitor good enough for you, or do you use something else? Time to let us know!