[s_baby]

I think Rackspace is using openresty.

http://openresty.org/

[pquerna]

Rackspace use hundreds of open source projects.

Luvit.io is specifically being used in our Host Monitoring Agent, which is open source and you can find here:

https://github.com/racker/virgo

This is used to collect all kinds of host metrics (CPU, disk, ram, custom scripts, mysql, etc) for the Cloud Monitoring Product.