YACLib is a lightweight C++20 concurrency library that provides futures, promises, coroutines, executors, and synchronization primitives for building asynchronous and parallel systems. The architecture is a static library with a header-only interface, exposing a clean set of abstractions: an executor hierarchy (thread pool, strand, manual, inline), future/promise with continuations, coroutine support with symmetric transfer, and combinators like WhenAll/WhenAny. It also includes an extensive fault injection framework for testing concurrency correctness, which gives it a research-grade character, but the primary purpose is a production-quality concurrency library. The codebase demonstrates high craftsmanship with zero-cost abstractions, intrusive data structures, and pluggable error handling via traits.
Sled is an embedded key-value store written in Rust that provides ACID transactions, crash safety, and high concurrency. It uses a lock-free architecture based on a lock-free pagecache, lock-free log, and lock-free B+ tree with epoch-based memory reclamation. The database supports multiple keyspaces, watch prefixes, merge operators, and a crash-safe monotonic ID generator. Currently in active development with a major rewrite underway (komora project), it is alpha software with known instability and frequent breaking changes, but demonstrates advanced concurrent data structure techniques.