Ultimate Continuity tester or Leo's ideal tool for continuity testing.
The design of the tool is described here: https://www.youtube.com/watch?v=N2M-p-OGvPg
A description of an implementation of such design can be found here: https://www.xul.it/blog/index.php/2020/08/15/the-ultimate-continuity-tester/
This repo stores the production files of the tool, with sources for Eagle and a Gerber export. All the files are released under the MIT license, with the permission of the original author.