Haproxy runs on Unix like OS (Linux, FreeBsd) and can be used to resolve all load balancing problem, of course even those Exchange Server 2010.
HAProxy is a free, very fast and reliable solution offeringhigh availability, load balancing, and proxying for TCP and HTTP-based applications. It is particularly suited for web sites crawling under very high loads while needing persistence or Layer7 processing. Supporting tens of thousands of connections is clearly realistic with todays hardware. Its mode of operation makes its integration into existing architectures very easy and riskless, while still offering the possibility not to expose fragile web servers to the Net, such as below :
You can visit the Steve Goodman’s Blog, where you can read how HAProxy works with Exchange 2010.