Jack Hughes over at The Tech Teapot posted today that Nagios has been forked. Apparently the lead developer (and sole person with commit access) has been very busy and not committing updates. This caused some self-described protagonists to launch "Icinga".
It's going to be very interesting to see where this goes. I personally hope that Nagios itself picks back up. My Nagios 3 installation is great, and I love it. I've had nothing but good things to say about it. If it doesn't pick back up, I have to wonder how many people will just move to OpenNMS.