Every IT professional always connecting directly or indirectly to IP address and sometime we need to calculate IP address for solution etc. So one of the best tool i ever seen is IP calculator.
IP Calculator takes an IP address and netmask and calculates the resulting broadcast,
network, Cisco wildcard mask, and host range. By giving a second netmask, you
can design subnets and supernets. It is also intended to be a teaching tool
and presents the subnetting results as easy-to-understand binary values.