Ask HN: Favorite IoT Fleet Management Tool/Service

I am looing for a suitable fleet management service - the application in use right now is Balena, but for my very little and cheap devices it is just too expensive. I mostly need OTA updates and the ability to update the core OS (rasobiaN). I also took a look at ubuntu core, easy to install and I guess I could build a service page myself that logs in, deploys a docker and so on ... are there any similiar services out there I missed (saw google, ms, dell, ibm, particle, fracctal ...)?