The Chosen Multi-Select Menu is an Umbraco 7 property editor based around the excellent Chosen.js jQuery plugin by Harvest. The Chosen Multi-Select Menu offers the ability to select one or more prevalue options from a drop-down list that you can categorize into groups and filter by typing, making it a snap to find what you're looking for, even with really long lists.
For documentation and examples, please visit the project page here: http://www.zweben.org/umbraco/chosen-multi-select-menu/
For more general information on the Chosen jQuery plugin, please visit Harvest's official Chosen project page here: http://harvesthq.github.io/chosen/