1. Mio: High-Performance I/O Library

If you're looking to create a high-performance I/O application with minimal overhead on operating system abstractions, Mio is an excellent choice. This fast, low-level I/O library emphasizes non-blocking APIs and event notifications. It supports non-blocking TCP/UDP, an I/O event queue using epoll, kqueue, and IOCP, along with platform-specific extensions. With over 5,000 stars on GitHub, it is a widely appreciated tool in the Rust community.

The first video titled "Writing a Library with Rust" delves into how to effectively utilize Rust for library development. It covers crucial concepts that can help you harness the full potential of Rust libraries.

2. Linfa: Machine Learning Framework

For those interested in machine learning applications using Rust, Linfa is a valuable resource. It serves as a library for statistical learning, offering algorithms for optimal model creation and density estimation. With various common algorithms such as elastic net, support vector machines, and linear decision trees, it has garnered over 2,000 stars on GitHub.

3. Regex: Regular Expression Library

Regular expressions are a staple for developers, and this library specializes in parsing, compiling, and executing regex patterns. It utilizes finite automata, ensuring linear time matching across all inputs. With more than 2,500 stars on GitHub, it's a reliable tool for string manipulation.

4. Syn: Rust Token Parsing Library

Syn is designed to parse a stream of Rust tokens into a syntax tree of Rust source code. While it's primarily intended for Rust procedural macros, it offers some APIs that can be useful in broader contexts. The library has over 1,900 stars on GitHub.

5. Indexmap: Ordered Hash Table

This library provides a hash table that maintains the order of insertion. It features compact map and set data structures, allowing for key lookups by either hash table key or numerical index. With over 1,000 stars on GitHub, it's an efficient choice for data storage.

6. Smallvec: Small Vector Optimization

Smallvec introduces a "small vector" optimization that keeps a limited number of elements inlined while utilizing heap allocation for larger datasets. This can enhance cache locality and minimize allocator traffic for workloads that fit within the inline buffer. It has garnered over 800 stars on GitHub.

7. H2: Asynchronous HTTP/2 Implementation

H2 provides an asynchronous implementation of both HTTP/2 server and client. It adheres to the HTTP/2 specification and is built around futures for its API. The implementation is decoupled from TCP or TLS specifics, requiring users to manage ALPN and HTTP/1.1 upgrades themselves. It has received over 1,000 stars on GitHub.