github.com/shabbyrobe/cmdy (go): Package cmdy is a self-contained library for implementing CLI programs.  cmdy combines the features I like from the flag stdlib package with the features I like from https://github.com/google/subcommands.  cmdy probably doesn't really need to exist, but I like it and use it for my own projects. There are a lot of CLI libraries for Go but this one is mine.  cmdy focuses on minimalism and tries to imitate and leverage the stdlib as much as possible. It does not attempt to replace flag.Flag, though it does extend it slightly.  cmdy has no dependencies beyond the stdlib.
Keywords: cli|go|golang|pure-go