Mixxx’s MIDI scripting engine is amazing. It lets you customize your MIDI controller to a level lower than almost every other DJ software.
A while ago, I made a pretty complex mapping for my M-Audio X-Session Pro. Buttons can perform different actions based on context. For example, holding the headphone button and then pressing another button will perform a different function than just pressing that button in the first place. If you press the headphone button without pressing another button, it will act as a normal PFL toggle button.
I then bought a refurbished Numark Total Control. It has lots of controls and status lights. The existing mapping that was in Mixxx was a bit old, so I decided to write a completely custom mapping. This mapping has a variety of interesting features. Buttons generally have two functions (press the “Key” button to activate the other function). There’s some good looping and hotcue support in there too. Furthermore, depending on whether you have vinyl control enabled or not, some of the controls will behave slightly differently to maximize functionality.
There’s a full table of the features on my Mixxx project page.
Lastly, I started designing a mapping for the X-Session Pro that would allow it to act as an auxiliary controller. This mapping primarily uses all of the buttons as hotcues, again with left and right shift buttons. It also has hotcues for the sampler. There’s a table describing all the features on the page.