If you've been working in the #Arduino ecosystem, it's probably time to check out #Zephyr OS. Under the banner of the Linux foundation, Zephyr is a free platform that won't be bought out from underneath you. (It's so good, that even Arduino announced they were adopting it, after their previous high-end-device platform choice died of Capitalism).

HMU if you want some pointers, Here's me a few years back talking about Zephyr: https://www.youtube.com/watch?v=TxsLPh5dF_s