A two-dimensional hash table that supports lookups by two keys simultaneously. It uses separate buckets for each dimension and provides insert, delete, and lookup operations. This is a non-trivial data structure that can be reused in any project requiring efficient two-key mappings.

A fixed-capacity circular memory buffer that supports enqueue, dequeue, undo (pop without deallocation), and duplicate operations. It is designed for variable-sized objects and provides efficient memory reuse. The implementation is clean and isolated, making it reusable for any FIFO or sliding window scenario.

A pre-allocated object pool with optional mprotect-based memory protection. It manages fixed-size objects in contiguous memory blocks and provides allocate/free operations with O(1) overhead. The pool can be configured to protect unused pages, useful for debugging or security-critical applications.

A type-safe string formatting library inspired by nginx's ngx_sprintf. It supports format specifiers like %s, %d, %x, %p, and custom types for IP addresses, times, etc. The implementation avoids buffer overflows by using a pre-allocated buffer and provides a chain of buffers for large output. It is a drop-in replacement for printf in constrained environments.