mimalloc is a compact general purpose allocator with excellent performance.

Linux namespaces and seccomp-bpf sandbox

Low-level unprivileged sandboxing tool used by Flatpak and similar projects

The seL4 microkernel

CUDA Open Source miner project, for most nvidia cards

Tup is a file-based build system.

A simple daemon to control fan speed on all MacBook/MacBook Pros (probably all Apple computers) for Linux Kernel 3 and newer

Command-line client code for Tarsnap.

A simple showcase how to create a simple OS X app in plain C without any Objective-C

Run nix in a lightweight chroot container

Complete DBus client library including bindings for C, C++, and lua.