Network scanner that always runs? Does it exist?

I'm looking for a program that continuously scans a set of subnets for any open TCP/UDP ports (at a low/configurable rate) or ICMP messages (any and all) - and feeds it to either something parse-able or something like an SQL. Google has delivered NMAP and a "super elite port scanners". I suspect NMAP might be a bit overkill and aggressive and still needs programming to deal with (which is fine).

Or has anyone seen script/source(s) (of basically any language) that would go a long way to get there? This is to detect misconfigurations and such. It does not need any detection of what actually runs there. Even half-way suggestions are welcome.