CheckYourNetwork.net - Free Online Network Checking and Testing Tools

Network Calculators - Network Calculators
    Subnet Mask Calculator, Network Node Calculator, IP Address Converter, Subnet Mask Inverter
IPV6 Network Tools - IPV6 Network Tools
    Various tools for checking an IPV6 network.
SubnetOnline.com - Various Subnet Calculators
    10 different kinds of network calculators, with each it's own purpose and look. No doubt that you will find one that will fit your purpose. From java to perl, from cgi to javascript.
phplabs.com - PHP epoch Date Calculator
    To determine the epoch timestamp for a particular moment in time, select the desired combination of year, month, day, hour, minute, and second:

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