We started the codebase that became Lucet in July 2017. It went through a few fast iterations, and by Jan 2018 we had Cranelift running with AOT compilation. In the early days of Cranelift that meant adding support for position-independent code output and filling in a bunch of gaps in the x86_64 encodings and other really low level stuff. At the time, wasmtime (under the name wasm-standalone, i think?) was a lot less mature, and wasmer was not public yet. So, in a sense, we did (& continue to) contribute to both of those runtimes via Cranelift and other dependencies like Faerie.

We spent the bulk of 2018 solving performance and integration problems, rather than cleaning up the codebase to the point where we could open source it. In the meantime wasmer was released, and both wasmtime and wasmer made a ton of progress. Now that our stuff is open source, it is easier for us to collaborate with other runtimes, possibly by moving more code back into the common Cranelift parent, or by adopting modules from each other.

I'm guessing Lucet was developed concurrently with the others, but unlike them, it had an extended period of internal development and testing first.