What are the best C-based utilities for the terminal?

I am working on a personal project, where I try to implement the features of a C-based utility, but in my own way, in my own project. I am trying to learn C, and I am learning a lot by reading what others created, and I am looking for some interesting ones to use.

I am looking for command-line based tools, written in C.
I don't know if this is the right forum for my question, but I thought that "programming" would be the appropriate location for a question that pertains to programming. :P

Thanks!