From the README.rst file at https://github.com/jkbrzt/httpie :

  HTTPie (pronounced aych-tee-tee-pie) is a command line HTTP client.

The name, as written on the repository, is "HTTPie", and not "Httpie" like in the title of this post.

H-T-T-Pie, which I'd relate to it being written in Python, where the file extension and several other names have "py" (pronounced as "pie") in some form.