1. Download the zip file to either your downloads folder or a user folder (C:\Users\(user-name). Unzip to the same place.
2. Right-click on the PetersTools.rhp file and select Properties. On the General tab, see if the file is blocked. (It'll say so near the bottom of the page.) If so, unblock it. This cannot be done unless the file is in your downloads or user folder. (Actually, I've heard that desktop works, too.)
3. It may work to drag & drop both files into the Rhino window. This is the easiest solution. If that doesn't work, try:
4. Copy the PetersTools.rhp file to your Rhinoceros 6.0 or 7.0 (64-bit)\Plug-ins folder.
5. Copy the PetersTools.rui file to wherever you like to keep toolbars.
6. Start Rhino.
7. Run PluginManager and press the install button. Browse to your Rhinoceros x.0 (64-bit)\Plug-ins directory and select PetersTools.rhp.
8. Load the toolbar that you saved by going to the Tools menu, pick Toolbar Layout, then File/Open the toolbar file.
9. If you then try to use the tools and encounter 'unknown command', go to Tools→options→plugins, check to make sure Rhinoscript is Enabled.

Download link for Rhino 6 and 7 users: https://www.food4rhino.com/app/peters-tools

Download link for Rhino 5 users: https://www.dropbox.com/s/zcjd1juurx2jrff/PetersTools1.93.zip?dl=1

Here's the Rhino 4 version, which may have different options… Download link for Rhino 4 users (I think this is the right file!): peterstoolsv1.25.zip

E-mail me with your questions and feedback on this plug-in. I get very little feedback, so anything I get really helps!