FretFind2D is a fretboard designer for microtonal and multi-scaled stringed instruments.
The latest version of FretFind2D is available for your use online.
Because FretFind2D does everything right in your browser, you can also download it to your computer for offline use. Please note, however, that FretFind2D will only be able to generate files if it is accessed through a web server. Thankfully there are a number of relatively easy ways to serve FretFind2D locally.
If you use the Chrome browser, I would recommend the Web Server for Chrome extension. Users of other browsers can follow these instructions for setting up a local server with Python from the Mozilla Developer Network.