If you don't have Maya and you do have Mac and you just want to play with the command-line version, you have to jump through several hoops:
You need to install XQuartz before trying to install Renderman. (Otherwise the Renderman installer will fail.)
You need to copy /Applications/Pixar/RenderManProServer-19.0/etc/rendermn.ini to ~/.rendermn.ini (Note the added "." in the front.)
You need to edit .rendermn.ini to add the line
You need to add these lines to your bashrc (or equivalent, depending on your shell.)
(Found on https://www.fxphd.com/kbslug/renderman/)
Once you've done that, you can use the "prman" command line tool to render rib files.