Windows only: Extended Task Manager —a robust Windows Task Manger replacement—will help you get a clear view of what is going on with your system, from random disk writing to locked files. Extended Task Manager goes above and beyond the basics of the default Windows Task Manger to give you information on disk activity, network usage, which ports are open, and more. All the graphs have mouse-over support, so if you see a spike in CPU usage, you just put the mouse over the spike and see which program was chewing up your cycles, and the same goes for disk usage and networking. If you're new to tinkering in the bowels of a task manager, check out our guide to mastering the Windows Task Manager; all of the principles there apply to the souped-up Extended Task Manager. If you're interested in trying out other task manager alternatives, take a peek at previously reviewed TaskExplorer. Extended Task Manager is freeware, Windows only.