UserAssistView is a compact portable tool which can tell you more about the programs that others may be running on your PC.
How does this work? Windows tracks when (and how often) you launch programs, leaving the details in the Registry UserAssist key. It's not about spying on you, this information is simply used to help Windows figure out which programs are used most frequently, so they can be given top billing on the Start menu. The data does also mean you can check to see which programs have been run on your system, though, and UserAssistView makes this very easy.
Just launch the program and you'll see several key columns: "Item Name" lists every program in the database, "Count" tells you how many times it's been used in total, and "Modified Time" tells you the last time a program was used.
Clicking on one of these column headers will sort the table accordingly, too. So, for instance, clicking "Count" will show you the most commonly launched programs on the PC, while clicking "Modified Time" reveals which programs have been used recently.
This can be very useful if, say, you're trying to make sure your kids really have been doing their homework rather than playing games, or you need to check what an employee is doing on a work computer. If you take the view that it's an invasion of privacy, though, you might like to wipe the UserAssist data on a regular basis: something like CCleaner will get this done for you (just check "User Assist History" in the "Advanced" list).
UserAssistView is yet another interesting system monitoring tool from NirSoft, and could be very useful if you need to find out how a particular Windows PC is being used.