Corey Butler's Fenix Web Server is a desktop web server for developers. The pitch:
Finally, a simple static desktop web server. Because simple stuff shouldn't need Apache, IIS, or Nginx.
It runs on Windows and OS X, has a boatload of features, and coolest of all: it accepts POSTs, PUTs, etc. and lets you browse the data payloads. This looks great for testing webhooks.