Thanks for the ping! We decided to use the same name (Wasmer) for the language embeddings as for the standalone runtime as we thought it could be easier for people to find related resources for the runtime. Hopefully is not too confusing! :)
Thanks for asking! I'm Syrus, I started the Wasmer project.
Lucet just released, but so far these are the current differences as far as I can tell:
1. Wasmer is meant to execute any WebAssembly file and run on any platform. Wasmer currently runs on Mac, Linux and Windows. Lucet only works on Linux at the moment, since its main goal is to be executed on Fastly's infra.
2. We support multiple compiler backends: dynasm, cranelift and LLVM. Each with a tradeoff between runtime speed and compilation speed (more info here https://github.com/wasmerio/wasmer/tree/master/lib#backends ). Lucet's architecture only supports one backend at the moment.
3. Wasmer has multiple interfaces/ABI integrations, including Emscripten, and soon WASI. Lucet initially shipped with WASI support, which is awesome.
4. Wasmer has a C/C++ API and its runtime can be integrated with other languages (C/C++, Rust and PHP at the moment)
That is a good summary! Lucet's runtime has a C API as well. We haven't created bindings to languages beyond C and Rust, but it should be pretty straightforward using the C API.
This is one of the main goals behind https://wapm.io :)