Tool for generating terse netmasks in several common formats.  If you've ever
maintained a firewall with more than a few rules in it, you might use netmask
to clean up and generalize sloppy rules left by the netadmin before you.  It
will also convert netmasks from one format to another for the day you change
your firewall software.

Homepage:
https://github.com/tlby/netmask/
