I figured out the problem I was having. This file is a .rar file, but its extension is .zip. Changing the extension back to .rar allowed me to open it (also, 7zip is able to open it even with the wrong extension, which may be what everyone else used). You might want to reupload it with the correct file extension.
This looks like a nice cute productivity tool. I understand it's far from finished, so there isn't much here to rate, but I like the idea. Good gems for good girls. :3