Did you know Anesthesia, Iodine, Penicillin, the Telephone, Photography, Mauve Dye, Nylon, Vulcanized Rubber are all accidental discoveries? I enjoyed reading the funny stories behind them and this reminded me of how I ran into or discovered (if I may call it so as it is on a different note than the profound discoveries mentioned earlier) the cool "Generic Handler" feature introduced in ASP.NET 2.0. I have found the feature extremely useful.
They're equivalent to custom handlers in that they contain classes that fully implement IHttpHandler but they are a lot simpler to use. A Generic Handler has a .ASHX extension. It is like a .ASPX page but it doesn't render a complete HTML page. It can be used to dynamically return specific content.
So dear Reader, have you discovered any hidden gems like this that have benefitted you greatly?