netcalc is a slimmed down clone of sipcalc, using the output format of ipcalc. It is written in C and has very few dependencies. Both IPv4 and IPv6 is supported.
The original sipcalc project was started by Simon Ekstrand in 2001. No longer in active development, but has a lot of features and is available on major Linux distributions and works on *BSD and Solaris.
Use GitHub to file bug reports, questions, feature requests or patches — preferably as pull requests!