I like the idea of a linux based CCTV system rather than a Windows based OS because I imagine it would more secure.
I found this, looks pretty cool:
https://zoneminder.com/
It supports IP cameras, Analogue cameras and webcams.. I think it also supports RS232 & RS485 along with I/O pci cards.
Here is a list of it's features and functionality:
http://www.tuxradar.com/content/build-your-own-surveillance-zoneminder
I haven't used this OS but if anyone has please comment on it..