Larry Stouts sample app and documentation 2015-05-05.zip
From Larry's main widget page...
Here is my entire application, which includes my Acme Widget. The Acme Widget is invisible, but adds key functionality to the basic Web AppBuilder viewer and modifies the appearance and/or behavior of several Esri Widgets (without editing the Widgets themselves).
NOTE: These widgets were written for an earlier version of WAB developer edition so may not work without modifications with current developer edition versions. Larry has changed jobs and is not working/updating these. They are as-is, with no direct support from Larry, but others in the forums might be able to respond to questions. If anyone does update, please share so others can benefit. Thanks.