LanCalculator - makes possible not only to easily calculate the subnet addresses range and subnet masks but also broadcast address, net address, net prefix and net mask inversion which is used in the access control lists (ACL) of Cisco network equipment. It is a freeware LAN calculation application that's well-designed and powerful.
Here is a screenshot to illustrate the features and user interface of this application:
NetLimiter
Network Monitor II
Network LookOut Administrator Pro
OpenVPN GUI
Psiphon 3