IPv6SubnetCalc is a comprehensive calculator for IPv6 addresses. It comes with Java Swing GUI and supports the following RFCs: RFC4291, RFC4193, RFC3849, RFC2464, RFC5375, RFC4941, RFC3513, RFC3879, RFC4941, RFC3056, RFC3587, RFC2374, RFC3306, RFC3956.
The Internet Protocol Address Calculator is an open-source java-based tool. This calculator will assist network administrators to perform calculations over both IPv4 and IPv6 address space. A handy whois search client is also integrated into this tool.