Probably the most used application on my Mac in times of crisis is Activity Monitor which conveniently displays all running processes and most importantly, those that have stopped responding.
atMonitor is roughly the same kind of tool with a few bonuses. As your Mac is running, atMonitor collects data in real time and displays it in the "Activity Viewer". This window floats on your desktop so it's unobtrusive and can be recalled a little quicker than starting Activity Monitor. More than this though, atMonitor can be used to specifically monitor selected applications and then export it to XML for further investigation.
For most general users, the most useful aspect of atMonitor will be that it displays clearly to which application every process corresponds to. atMonitor displays the name, description, full path, environment and ownership of each process. It's also a highly customizable app in terms of both the way it looks and what it monitors. Perhaps the only annoying thing is that when you start atMonitor, you're only presented with the tiny activity monitor. It took me a while to work out that you have to Cmd-click the dock icon and select "Top" to view the main activity monitor window.
atMonitor is a handy tool to keep a discreet tab on your Mac's performance without having to resort to the Activity Monitor.