"MINIX predates L4 and has evolved independently."

Minix 3, a new system with the same name, doesn't predate L4. Tannenbaum probably learned stuff from the L4 people given he cites their work in his microkernel debate with Torvalds. They made a custom kernel since their requirements were different than L4 people's. They might have also thought it would be fun. Lots of researchers like just doing their own thing for the experience.

"L4 has had quiet success in the embedded space. "

Don't understate it: OKL4 claimed deployment in a billion phones mostly for baseband isolation. Got acquired by General Dynamics for big bucks. So, there's one, success story.

Not big bucks, it was broke, general dynamics shut it down shortly after. Nobody with options got paid. The claim of a billion phones should be taken with some salt and l4 wasn't being used like a microkernel on the baseband - everything running in protected mode. If okl4 is the benchmark of success, microkernels are a near total failure. OKL4 was an abject failure, he said bitterly.

Oh wait, it looks like I missed his write-ups looking back at the company since I transitioned to a new area. I'll be going through them later. Thanks for the correction! So, I drop claims to L4 mostly a failure so far with other microkernels being successful in niche markets, esp embedded and safety/security-critical. The L4 people at places like Dresden at least gave us lots of good designs that are being put to use in open-source and commercial works. Device, driver VM's and Nitpicker GUI come to mind.

EDIT: Still reading the articles. Gernot reminds me PikeOS from Sysgo was "a L4 clone." They got acquired by Thales after quite a few iterations on their PikeOS product. An annual report I found by Thales said they were acquired for over 20 million Euros. Still on low-end in terms of market value but might have been successful depending on money in vs gained.

EDIT 2: Read his blog posts. Before OK Labs Post No 6, here's what he claims about L4 uptake:

"Secondly, a lot of stuff is running on L4: – Qualcomm modem chips have been running our L4-embedded kernel since 2006, that’s a few billion devices – The security processor of all iOS devices is running a modified version of our L4-embedded, that’s another 200-300 million devices every year – seL4 is being deployed on autonomous military air and ground vehicles, with the first autonomous helicopter flight in July 2015 – many other safety- and security-critical deployments are in progress.

I’m not aware of any real-world deployments of Minix."

Of course, we found out later Minix 3 was in Intel's baseband. So, there's two of them with people claiming massive deployments in supporting CPU's/MCU's. What you alluded to didn't refute a large number of units. Just that the company was anything as good as marketing presented. It wasn't. A few deliverables kept selling, though, per same source. He was wrong about Minix 3, too. Probably because it was Intel's secret for a while. I bet they wanted the reliability, included apps/code, and BSD license.

Definitely treat anything written by Heiser like any other marketing document, identify his interests at the time of writing first. And sure you can say that for almost anyone in this business...