mulle-concurrent provides a few wait-free/lock-free datastructures. The underlying platform thread library is abstracted using mulle-thread. The problem of thread-safe memory reclamation is handled by mulle-aba.
The mulle-concurrent library collection is written for C11, but has a fallback for compilers that don't provide atomics.
mulle-concurrent is based on mulle-c.
The mulle-objc runtime is based on mulle-concurrent.