There are hundreds of keyboard models available for sale these days. There are keyboards with mechanical and dome switches, models with and without Numpad, keyboards with card readers, and trackpads. But there are no modern keyboards with a vintage rotary phone dial that serves as a Numpad. But apparently, it is possible to build one yourself.
The Rotary Keyboard project by Squidgeefish (via MiniMachines.net) is not precisely meant to enable new functionality or increase productivity but rather to make an Aprils Fool prank. Unfortunately, for the same reason, the keyboard lacks its Numpad and numeric row to make the prank work.
Arguably the biggest challenge with attaching a vintage rotary phone dial to a modern device is that it is analog and produces a pulse train instead of a signal. By contrast, modern keyboards are digital, so there is no way to make the dial work without installing any additional parts. So Squidgeefish took a DFRobot Beetle Board based on the ATmega32U4 chip, which has ten digital pins, five analog pins, and four pwn pins and can be programmed to read a pulse train with a simple program while still maintaining compatibility with a standard USB interface.
Physical installation of a rotary dial also looks quite challenging, as it entails cutting a printed circuit board without knowing which traces go where. Yet, after several attempts, the modder managed to make things work. To make the keyboard look more or less aesthetic, Squidgeefish had to 3D print some parts, including the dial and the replacement for the numeric row, which had to go to make the dial worthy.
The result looks strange, but it works: the dial can input numbers and symbols. Of course, it has nothing to do with steampunk keyboards with typewriter-style keys, but this was not the project's point.
The entire cost of the project was probably lower than $30, but it certainly took a bunch of time to assemble it and make it work.