You mean mBad?
"ARM has told us it is trying to open source as much as it can – using the Apache 2.0 license – but commercial realities cannot be ignored."
The commercial reality being that every IoT vendor wants to slurp up your personal data to their "private cloud" and sell it off to the highest bidder, etc.
Joking aside, at least they have the client that is completely open source. So here's hoping you really can write your own backend. Of course that's after the inevitable cat and mouse game of vendors trying to lock down all their devices in the name of trust! and security! while people find a way around it so they can install truly trustworthy software stacks and actually apply security updates.