petere/c-ares

c-ares is a C library that lets programs look up web addresses (DNS queries) without freezing. Normally, when an application asks "what's the IP address for google.com?", the program has to wait for an answer before doing anything else. c-ares flips this around, it lets you ask the question and then immediately move on to other work while the answer comes back in the background. This is especially useful for servers handling many clients at once, or for apps with a user interface where freezing would feel sluggish. The library works by handling DNS lookups asynchronously, meaning you can send multiple address-lookup requests at the same time and process their results whenever they arrive. You don't have to sit around waiting for each one to finish before starting the next. This matters a lot in real-world software: a web server talking to thousands of clients, or a desktop app responding to user clicks, can't afford to block and wait for network answers. The project is a maintained, well-established C library, it's mature enough to be included in major open-source projects and follows security best practices. If you're building system-level software in C that needs to talk to multiple services or handle many concurrent connections, this library solves the "don't block on DNS" problem for you. It's distributed under a permissive MIT-style license, so it's free to use and modify. The README notes that this is a fairly low-level, systems-oriented project. It requires building from source on your platform, and the maintainers keep strict standards around code style and compiler compatibility, they assume only basic C features so the library works everywhere from old embedded systems to modern servers.