picolibc
A small C library for microcontrollers, stitched together from newlib and AVR Libc with the aim of being both leaner and more modern.
Keith Packard, better known for his work on the X Window System, started picolibc in 2019. He kept newlib's maths and string routines, replaced stdio with a compact implementation rooted in AVR Libc, and cleared out code with awkward licences so the whole thing ships under BSD-style terms.
The key technical difference from newlib is how state is held. newlib gathers per-thread data such as errno into a large reentrancy structure; picolibc uses thread-local storage, which is smaller and much easier to get right under an RTOS. It has been Zephyr's default C library since 2023 and is offered as an option in several cross-compiler distributions — a brisk career for a library in an industry that changes tools about as often as it changes soldering irons.