Varnish is a great example of modern software programming techniques. It is a caching reverse proxy designed for high-traffic sites to alleviate loads on back-end servers. It supports a wide range or request rewriting and modification. It also includes load balancing and fail-over mechanisms as well as grace periods where stale content can be served in lieu of a back-end connection failure. Here's why I'm featuring it on our Software Rebirth blog:
First of all, it is open source. Need we say more?
Second of all, it is designed for modern systems. It runs well on modern operating systems like linux 2.6 / GNU and FreeBSD 7. It leverages characteristics of the kernels to keep itself simple in design.
Lastly, and perhaps most importantly, the architecture and design is well thought out and documented, so that those who question the design decisions can refer to its plan.
I'm a huge fan of Varnish because I use it on my servers and it has served me well, no pun intended.
More information about Varnish: