Here's a port of my FlexViewer Closest Facility Widget for the Web AppBuilder.
http://www.arcgis.com/home/item.html?id=9a81bb2f4d7c416d8eaca4fe2864c910
Try it live here or get the code here.
Changes:
v1.1.5, 1/21/2016:
- Fixed a problem in which some facilities datasets with lots of attributes confuse the solver. Create a copy of the facilities, but without attributes, before sending to the solver.
v1.1.1, 1/15/2016:
* Settings page: animation duration field now forces the value to be a nonnegative integer
* Displays a busy indicator while the server runs the solver