Cross-platform asynchronous I/O

The LLVM-based D Compiler.

The LLVM Project is a collection of modular and reusable compiler and toolchain technologies.

Converts floating point numbers to decimal strings

a clean C library for processing UTF-8 Unicode data

libunwind official github repo (in need of new / additional maintainer, mail/open issue if interested)

Frame profiler

Intel® Instrumentation and Tracing Technology (ITT) and Just-In-Time (JIT) APIs

Double precision SIMD-oriented Fast Mersenne Twister

High quality system independent, portable, open source libm implementation

Using PLT trampolines to provide a BLAS and LAPACK demuxing library.

nghttp2 - HTTP/2 C Library and tools

the SSH library

The official SuiteSparse library: a suite of sparse matrix algorithms authored or co-authored by Tim Davis, Texas A&M University.

PCRE2 development is based here.

7-Zip

A massively spiffy yet delicately unobtrusive compression library.