Windows Task Manager, useful for viewing a computer’s performance or ending stubborn processes, has a default setting ‘Always on Top’ and a strange view that will remove the border. This still allows you to move the window around but removes your ability to close the window (unless you were to kill the taskmgr.exe process). This ‘strange view’ has existed since at least Windows XP and still exists in Windows 7.
The border-less view is the same dimensions as the normal window and only allows you to see a few more processes in the list. To get out of it and get back to the normal view that will give you a minimize, maximize, exit button and the menu bar, double-click on the white area framing the information. Your coloring might differ based on your Windows theme; between the buttons, around the list, or next to the scrollbar will all work just fine. Just double-click it and you can get your normal task manager window back.
This makes me think of Internet Explorer’s full-screen mode. When using IE as your browser, you can hit IE to get a full-screen. I’ve received many tech support calls in the day where “something is wrong with IE” and it can be toggled off just by hitting F11. Somehow the person made the change but didn’t realize what they did to make it happen. Similarly with the task manager, to get into the borderless view, you double-click the frame around the process list (or other tabs) and it will toggle between the two views.