Open Source development library (API)

ADKH

I am looking for a open source development library (API), so I can create my own developed synthesizers that can be connected to Native Instruments applications. Much like C++ development connecting to Reaktor. Like connecting components inside the Reaktor together.

Paule

Something like Dr Sync (Vadim Zavalishin) built as SynC Modular?

https://www.musicradar.com/news/blast-from-the-past-sync-modular

https://www.adsrsounds.com/useful-articles/vadim-zavalishin/