Jon Langberg is a long time guitar player. In 2014 he realized that a banjo would be perfect to play a specific song but didn't have the time or money to find one. He began to develop a method that could take his guitar and modify it to make the sounds of a banjo. Langberg is currently running a crowdfunding campaign for GUITAR-JO, a device that attaches to electric guitars and produces a banjo twang.
Langberg noticed that adding fabric to dampen the strings vibrations gave him the sound that he wanted, and worked to develop his fabric dampening device. After several iterations and changes in shape, size, and string placement Langberg developed the current design for the Kickstarter. The unit is placed on the top of the guitar and then each dampening pad can be individually adjusted to tone each string. The campaign page notes that this system works for flat guitars only, and electric guitars only. Les Paul is one of the brand that is called out specifically for not being suitable for the device because of Les Paul's rounded surface underneath the strings. The device is made from ABS, acetal, and standard fasteners. No durability or environmental testing is mentioned in any of the material I've found online.
Two great things jump out at me with regard to this engineering story. First, Jon made an extensive search for a software or digital filter that would give his guitar the sound that he wanted but nothing worked for him. That's when he decided to move forward with a physical solution. Next, this is a hyper specific application - he developed the GUITAR-JO device thinking he was the only one who needed a guitar-to-banjo interface, but the more he plays it the more he realizes a wider possible utility. Langberg has filed for a patent and hopes to build more music tools in the future. The campaign ends on January 9 and if successful first units are expected to ship in February 2018.