FREE IP Subnet Calculators
Classfull, CIDR

Web-based calculators.

3CIPCalc

IP Subnet mask calculator from 3Com.

ipsubcal.zip

Simple IP Subnet mask calculator.  Does not need to be installed, just unzip and run.

ipcalc.zip v1.02

Net3 Group's IP Subnet mask calculator.  Does not need to be installed, just unzip and run.

ipcalc2.zip v2.02

Net3 Group's IP Subnet mask calculator.  Must run a setup program.

Hymie's IP Subnet mask calculator

For the Palm Pilot.