fidius
Plugin systems in Rust usually mean writing FFI by hand: raw pointers, extern "C" shims, manual versioning, and plenty of room to get it subtly wrong. fidius removes that. You define a plugin interface as an ordinary Rust trait, annotate it, and the macro generates the ABI shim, the version hash, and a typed proxy the host calls through. The plugin compiles to a normal dynamic library; the host loads it and calls it as though it were local, with the compiler checking both sides.
A fidius system is three small crates: an interface that holds the trait, a plugin that implements it as a cdylib, and a host that loads and calls it. The CLI scaffolds the first two, so the only code you write is the trait and the impl; the FFI in between is generated. Because the ABI is versioned and hash-checked, a host can tell whether a plugin really matches the interface it expects before it calls anything, and an interface can grow over time, gaining optional methods, without breaking the plugins already in the field.
Trust is built in rather than bolted on. Plugin artifacts can be signed and verified with Ed25519, so a host can refuse to load anything it cannot vouch for. Plugins are not limited to Rust either; a Python plugin can satisfy the same Rust trait through the Python bindings.
The name is Roman; Fides was the goddess of trust and good faith, the keeping of one’s word.
fidius is open source under the Apache 2.0 license.