This is the best summary I could come up with:
Microsoft is open sourcing the realtime operating system that it acquired with Express Logic, donating it to the Eclipse Foundation.
As soon as this innocent little OS turned 21 in 2019, Microsoft grabbed it, acquiring ThreadX owners Express Logic and rebranding the poor thing as Azure RTOS, which hasn't done any favours for its brand awareness.
After the purchase, original developer William Lamie left, starting a new company which sells a "fifth-generation" RTOS with POSIX-compatible threads, called PX5OS.
Even so, ThreadX is a tested and established product; some parts even have TÜV Functional Safety (FuSa) certification, such as the STM32 version [PDF].
Although the GPU drivers have long been open source, the firmware never was, and attempts to write an independent FOSS version were never completed, for reasons explained on the project page.
As of last year, the foundation had sold over 46 million of the things, and if the whole software stack were open source, that would make them even more appealing for a lot of people.
The original article contains 603 words, the summary contains 168 words. Saved 72%. I'm a bot and I'm open source!