HAProxy is a free, open-source load balancer and reverse proxy that is fast, reliable and offers high availability. It can be used to load balance HTTP and TCP-based applications. Some key features include out-of-band health checks, hot reconfiguration, and multiple load balancing algorithms. Many large companies use HAProxy to load balance their websites and applications. It runs on Linux, BSD, and Solaris and can be used to load balance applications across servers on-premises or in the cloud.