Mac OS X, as it ships or gets installed from an Apple DVD, is a mighty impressive operating system, but different people use it in different ways.

While many people will never even think about modifying the behaviour of their systems, there are many more who will want to do exactly that. If this is you, you'll be interested to learn that there are a large number of excellent tools for tweaking OS X and altering the way it works, the majority of which operate non- destructively.

There are also some great monitoring and system maintenance tools available that go way beyond what Apple gives you as standard, and these can help you on your way to keeping a clean and healthy operating system that lasts a long time. Here are some of the best.

iStat Menus
Freeware, Mac OS X 10.4+
You may not be aware that your Mac contains many logs and sensors, most of which aren't immediately accessible without help. This help is available for free in the form of iStat Menus, a program that puts eight configurable menus at your fingertips in the menu bar. These menus will monitor crucial parameters such as CPU usage, disk activity, network traffic, temperature and processes. For troubleshooting, or simply a better way to understand the workings of your Mac, iStat Menus is an invaluable tool, and you needn't be a technical whizz to use it successfully.

Onyx
Freeware, OS X 10.2+
OnyX is a comprehensive system-tweaking and maintenance tool that gives you unprecedented control over the way your Mac behaves and displays windows, buttons and menus. It also contains extensive cleaning commands for clearing caches and logs, repairing permissions and running maintenance scripts. OnyX puts these commands at your fingertips. One particularly useful option is to view hidden files and folders, which can be crucial for troubleshooting

MenuMeters
Freeware, Mac OS X 10.2+
There are many small applications that will monitor your Mac's core functions and activity, but of all these tools, MenuMeters is the most compact and unobtrusive one we've used. Controlled via a Preference pane, you can activate monitoring of CPU, network, disk and memory usage, and these will sit quietly in the menu bar, letting you see at a glance what's going on. A simple mouse click will display expanded statistics.

Amnesty Singles
$10, Mac OS X 10.3.9+
Mac OS X 10.4 introduced widgets that are pretty cool, but they have to be "invoked" and seem to live not on the Desktop itself, but somewhere above it. If you'd like to alter this floaty state of affairs, a dedicated application will let you do just that. Amnesty Singles is a program that enables you to convert widgets to standalone applications, simply by dropping your favourite widget onto the program and clicking a button – it's that easy. This turns any of your widgets, be it Dictionary, Calendar or Ski Report, into mini, standalone applications, making them much more flexible.

Renamer4Mac
Freeware, Mac OS X 10.3+
If you ever have to rename more than a couple of files at once, you'll realise what a tremendous pain it can be as you click in their name fields over and over again. Renamer4Mac is an excellent free program which lets you batch-change filenames in many ways, including search and replace text, insert/overwrite, number files and convert upper or lowercase. It's an incredible timesaver.

Temperature Monitor
Freeware, Mac OS X 10.3.8+
Modern Macs incorporate multiple temperature sensors, and this program is able to read them and provide you with a real-time display and graph of how hot each part of your Mac is getting. While Temperature Monitor doesn't actually modify your system, it can be key to identifying trouble spots within the computer or working out where best to position the Mac in the room for optimum temperature and performance.