Common, everyday stuff
Functions for reading and writing files. Abstractions for working with directories and file paths.
Higher-order functions (map, filter, reduce, etc.). Specialised data structures for functional programming (e.g., immutable lists). High performance clone of lists, etc.
Custom memory allocation and deallocation functions. Memory pooling or slab allocation for optimized memory usage.
String manipulation functions (concatenation, substring, searching). Regular expression support.
Mathematical functions (trigonometry, logarithms, etc.). Random number generation.
Basic networking functions (TCP/UDP socket creation, sending/receiving data). URL parsing.
Threading and synchronization primitives (mutex, semaphore, etc.). Thread pooling or task scheduling.
Date and time manipulation functions. Timer functions for measuring elapsed time.
Custom error handling mechanism. Functions for retrieving error messages.
Configuration file parsing (INI, JSON, XML, etc.). Access to environment variables.
Compression and decompression algorithms (e.g., zlib). Basic encryption and decryption functions.
Parsing command-line arguments easily. Options for handling command-line flags and parameters.
Functions for converting data structures to/from a serialized format (JSON, XML, binary).
Input validation functions for common data types. Regular expression-based validation.
Higher-level abstractions for managing concurrent tasks. Thread-safe data structures.