Play around with the Windows user interface
Tweak UI enables you to change some particular settings of Windows user interface, some of which you probably didn't even know they could be changed at all.
The program uses a tree-like structure to display the elements you can customize that makes it a bit messy when all of them are opened. Each element includes a detailed explanation so that you're sure about what you're doing before changing anything, mainly because there's no "Undo" option.
In any case, most tweaks are applied to visual settings and small graphic details, so they won't make your computer crash if anything goes wrong.