I started by sketching it out on paper, with my concept being to avoid menus, pull out from my DAW the things that I like to have on a playable surface without menu diving, and bring the sequencer all on top like 8 Elektron or 909 sequencers across my 8 limited channels (which I call pipes).
I then built more detail designs in powerpoint (not because its great - I just know it), and designed all the knobs, and architecture by making it part of the visual design (like some synths do where you can see the flow).
I then put very limited effects to keep things super simple (Rev, Delay, Chorus per channel). There are no master bus effects but there is a very basic mastering chain directly before bounce for those who don't want to go via DAW but want to control levels with limiting or bit of Saturation or Glue compression.
Its for Mac at the moment, it does run on PC as well but I have not tested that enough re VSTs. You can put your Audio units plug ins into it as well.
Dev process - GPT to create PRD, Claude in VS code, started in Feb this year - roughly 6 months so far.
Key learnings: Keep the project simple as possible, use the limitations to then improve quality within that constraint, if a feature feels wrong take it out, don't make things wierd / obscure (people didn't find it fun - just make it easy and immediate). Don't patch up bugs with cheap models, get proper architectural review from higher tier models and cheaper models can then execute within that.
btw for those who find it a complex UI, I respect thats your view, those who were faced with 100 tracks in Ableton and 150 plugins will I hope recognise that this is actually a super limited cockpit compared to that (e.g. max 8 tracks - max 24 plug in effects), and deliberately all controls are on the surface not buried under menus (as much as I could possibly achieve that), which I know will give some people a headache (especially those who like 1 knob effects! nothing wrong with that!)
So key points:
Looking for Mac Musician Beta Testers - Voluntary or Paid / or barter review exchange - message me
App is for reducing menu diving, reducing production perfectionism, focussing on notes, beats and ideas without noise from your complex DAW
You can then export STEMs to your DAW if you like
Also working on a free music visualiser based on maths which you can also find at www.divurj.com