HAProxy is a free and open source software that provides a high availability load balancer and reverse proxy for TCP and HTTP-based applications that spreads requests across multiple servers. It is written in C and has a reputation for being fast and efficient (in terms of processor and memory usage).

HAProxy is used by a number of high-profile websites including GoDaddy, GitHub, Bitbucket, Stack Overflow, Reddit, Slack, Speedtest.net, Tumblr, Twitter and Tuenti and is used in the OpsWorks product from Amazon Web Services.

https://en.wikipedia.org/wiki/HAProxy