DarkAudacity is a mildly redesigned edition of Audacity, the classic Windows audio editor and recorder.
The program is a branch of Audacity rather than a fork, so shares the same code base. It has no big technical differences to the original project - no extra effects, no expanded file format support - and is instead more about revamping the interface to give it a more modern look and improve ease of use.
For example, as the name suggests, the colour scheme is a little darker and there are new Material Design icons.
The top level menus have been shortened and redesigned, with lesser functions relocated to submenus.
Panels and the meter have had surplus numbers removed to cut down on visual clutter, so you're no longer forever looking at "Stereo, 44100Hz 32-bit float".
There are small practical changes. For instance, previously many functions were disabled when the Pause was down, and you had to switch out of that mode to use them. Now you can just select any of these "disallowed" features and DarkAudacity automatically pops up the Pause button and stops recording or playback.