pfSense

Probably too much computation to do for a widget, and maybe even too much to do automatically for the leases view, since this would have to be done by parsing the entire leases file and matching up lists of IPs with each configured pool. Perhaps a checkbox option like exists for the DNS resolution of ARP entries.

Keep in mind that some people with large and busy networks can have lease database files that are extremely large, so while this would work fine for small-ish networks, it would not scale well.

Unfortunately the DHCP daemon doesn't have a way to get the info directly, it would be handy if it exposed the info over its omapi interface or similar status query output, since it has to be keeping track of it internally already.