[harpocrates]

What other low-level format supports my points (a), (b), and (c)? And has an actual spec?

EDIT: you've since added some examples. Here are my (very subjective) opinions:

- The JVM isn't really all that low-level - it eeks out a lot of performance at runtime. Plus, you need to have GC, which tends to increase memory requirements and complicate real-time constraints.

- NaCL was interesting but its spec wasn't as good. IIRC Google didn't do too much in the way of asking for public input. I think some folks had some security concerns too. I really like WebAssembly's spec - I don't see any typing judgements or small-step rules for NaCL.

- Wasn't ANDF unix-bound?

[pjmlp]

Mesa in Xerox Star, TIMI in IBM i, Language Environment on IBM z, MCP in Unisys ClearPath, UCSD Machines are some of the most well known examples.

Using bytecode as portable executable format has been a tradition in mainframes since the early 60's.

[fulafel]

As far as I know, all of them match WebAssembly on those points. Though most are far back in history and not current rivals.

[protomyth]

UCSD p-machine?

[e12e]

I'm not very familiar with the various jvm profiles - but isn't javacard pretty light? (the stuff that runs on similar cards and such)?

[imtringued]

Yes but you're still bound to java semantics. Java is very high level. Almost everything except the blessed primtives long/int/short/byte is an object. This is not a suitable target for lower level languages like C.