EventSentry Light is a powerful tool that can monitor your Windows event logs (and system health), alerting you to any problems.
If you're a Windows expert and want to be warned if a particular event type occurs, for instance, then you can have the program display a message or send you an email.
A Software Monitoring option allows the program to log when software is installed, or uninstalled (useful if your PC has several users and you'd like to track what they're doing). And it can also record programs that have configured themselves to load when Windows launches.
A Disk Space monitor is able to alert you when the free space on a drive gets too low (you get to decide what figure that might be). Or it can check a particular folder, alerting you when its size exceeds or falls below a particular limit.
And the Performance Monitoring module can track your PCs CPU or memory usage, again logging the details if something's hogging all your resources.
If you need even more power then opting for the commercial edition will get you the ability to manage more than 2 remote computers, with web-based reporting and iPhone/ Android apps. Command line tools support automation, there are full software and hardware inventories, and if you have any problems then you can call on phone, email and even "getting started" support. Prices start at $85 per host, and the EventSentry site will tell you more.
Version 4.0.3 (changelog).
Management Console: Fixed regression bug from build 188.8.131.52 that would cause remote agents to ignore configurations updates sent by the collector