There are really only two popular Rust libraries that use unstable features:
1. serde, the best serialization/deserialization library. This works on stable now using the `serge_codegen` crate and a custom `build.rs` script. This will Just Work on stable with no extra setup once Macros 1.1 lands, theoretically in about 5 weeks. But I'm using it on stable now in a half-dozen projects, thanks to a `build.rs` script.
2. Diesel, the high-level ORM library for Rust. This works on stable using a `build.rs` script, and 90% of it will work on stable without the `build.rs` script once Macros 1.1 ships.
There are a few other experimental libraries like Rocket (which looks very slick) that only work on nightly Rust. But I don't think any of them are particularly popular yet.
Personally, I maintain something like two dozen Rust crates and applications, and only two use nightly Rust. Both need Macros 1.1, which should be on stable in about 5 weeks.
serde works on stable without serde_codegen or custom build scripts, too. It works like a regular library in fact, just with less features (no code generation feature). A custom data structure might not be able to use the default code generation for its impls anyway.
1. serde, the best serialization/deserialization library. This works on stable now using the `serge_codegen` crate and a custom `build.rs` script. This will Just Work on stable with no extra setup once Macros 1.1 lands, theoretically in about 5 weeks. But I'm using it on stable now in a half-dozen projects, thanks to a `build.rs` script.
2. Diesel, the high-level ORM library for Rust. This works on stable using a `build.rs` script, and 90% of it will work on stable without the `build.rs` script once Macros 1.1 ships.
There are a few other experimental libraries like Rocket (which looks very slick) that only work on nightly Rust. But I don't think any of them are particularly popular yet.
Personally, I maintain something like two dozen Rust crates and applications, and only two use nightly Rust. Both need Macros 1.1, which should be on stable in about 5 weeks.