There's Open Firmware, which runs on a portable Forth interpreter. That was supposed to be a standard for board setup code. But proprietary systems won out. It was too open.
Bedrock is a lightweight program runtime: programs assemble down to a few kilobytes of bytecode that can run on any computer, console, or handheld. The runtime is tiny, it can be implemented from scratch in a few hours, and the I/O devices for accessing the keyboard, screen, networking, etc. can be added on as needed.
I designed Bedrock to make it easier to maintain programs as a solo developer. It's deeply inspired by Uxn and PICO-8, but it makes significant departures from Uxn to provide more capabilities to programs and to be easier to implement.
Let me know if you try it out or have any questions.