In the beginning of January 2022 I had a bad cold but also really wanted to start DJ:ing. I had previously used the app TouchOSC to remote control Ableton and figured you could probably build a DJ controller with it too.
I looked around and found the excellent software Mixxx which is open source and scriptable, allowing you to create complex mappings for pretty much any controller. Together with TouchOSC this allowed me to build a fully functional DJ controller with only my laptop and iPad.
Here's a mix I recorded using the setup. I have since gotten a proper controller and am playing out live but I think this proves that DJ:ing requires almost nothing, and that selection and technical skills are what makes or breaks a mix. I might one day try to build a tiny minimal controller you can everyday carry, for when you visit a friend and wish you had your controller with you.
The final layout as found on the GitHub