IP Subnet Calculator Widget will calculate the Network Address, Broadcast Address, and number of hosts in a subnet given an IP address and Subnet Mask.
Subnet Mask may be entered in either dotted decimal notation or directly in number of bits masked.
You may also click on the Subnet Mask button to change to the Wildcard Mask view. Click again to go back to the Subnet Mask view.
Version 1.5 fixes a bug in 1.4 where pressing enter in a field would cause both the Subnet Mask view and the Wildcard Mask view to appear and throw off the layout of the widget.
Mac OS X 10.4 or later
*Previously available here