Windows Tweaker is a free utility. Although this is a desktop utility, it has the clean modern look often found on mobile apps. There is a portable version as well as an installer version. The portable version is 0.85 MB and the installer version is 2.45 MB. I tried both and I see no particular advantage to the installer version except that its performance was a little smoother.
The program requires the .NET 4.5 Framework. Because it can be used to make changes to the system, it requires administrative privileges to run. One annoyance is that it opens in maximized view, taking up the whole screen like a Windows 8 store app. The view can be changed to a smaller one by toggling the maximize button in the upper right corner of its window. You can then see part of the desktop but further re-sizing can be done only from the right side of the window.
There are said to be 100+ settings available and the screenshot below shows some. As the graphic shows, a pane on the left side lists 11 categories of settings. When one of these is selected, tabs across the top of the window with sub-categories are displayed. Selecting one of these then shows a list where you can select various possible tweaks. In the graphic below, the category “Explorer” has been chosen and the tab “Start Screen” selected. There is also a search function to make finding a particular tweak easier. If you would like to see more examples of which tweaks are available, the website link below will take you to a collection of screenshots.
Before making any changes to a system, it is always a good idea to make a backup and the utility has an options button (lower left corner in graphic above) that opens a menu containing an entry that will let you create a system restore point.
Link to Windows Tweaker Website