Here is a concept instrument which I created in Xpressive. There are a number of different waveforms mapped to MIDI keys. Since the pitch isn't controlled directly by the key, A1 controls the pitch offset from 440 Hz, and A2 controls the decay.
Originally, A3 was intended to control frequency modulation (FM) or amplitude modulation (AM), with a 50/50 mix depending on the key. However, I made modifications and A3 now adjusts the frequency of the second waveform that's added within each key. I've kept the original FM/AM version in O2, zeroed out at zero volume, as it might still be useful, though I personally found it didn't produce as many interesting sounds.
You can place random notes (and multiple notes) between, and inclusive of key 36 and key 75 in the piano roll. A1, A2, and A3 can then be controlled using the automation editor, which allows for the creation of some truly interesting sounds.
I had at various times heard music that sounded like a selection of sampled short waveforms where I always wondered how I could sequence from a bank of samples or wavelets and manipulate these on each bar to make the music interesting and not just some random loop (as I never owned a professional sampler).
So, this is what I came up with. Maybe it is useful. Maybe it is not useful at all. I did have additional ideas such as the ability to control the length on and off for each waveform (almost like a cross between a gate and pulse-width modulation noting that the waveform is not a pulse). However, I was limited to three dials (A1, A2, and A3) and the mathematical expression was already getting quite complicated without the allowance to used named variables or comments to keep track of my changes.
Maybe this will be a good starting block for someone who wishes to expand on the idea. As Xpressive can be used as an arbitrary waveform generator and allows control of three variables in each waveform, the possibilities are endless. However, time would be the biggest constraint in creating interesting wavelets or waveforms, along with the chance of each actually being useful together with the others musically.
I also had the idea of creating a GM-mapped SID style drum kit for Xpressive where each MIDI key would be mapped to a mathematical expression for a drum. This could be used in place of a sound font for MIDI mapped drums. I realised that I couldn't use my previously created 808-style drums because each one required a different LMMS filter external to Xpressive. I eventually gave up due to the sheer number of drums I'd have to create.