Evcxr is a Rust interpreter and also provides a Jupyter kernel. This is a helpfull addition to the online playground as it allows installing and using any crate.
These websites provide tools which convert JSON data to structs in different programming languages.
The Rust API guidelines explain conventions around naming, interoperability, and documentation for libraries. It provides a helpful checklist for all important points.
The Rust Cookbook describes tiny common tasks you might want to do and shows how to solve them in Rust. It introduces many usefull crates, which are widespread in the Rust ecosystem, but can also be used to look up solutions to common problems.
Helps in understanding macro_rules macros by automatically generating syntax diagrams for them.
Rust regulat expression editor and tester.