alphashot is a web-based screenshot tool that can capture windows with transparency and shadows. Works with Windows. It works by taking 2 screenshots, one on black and another on white. It then combines the two images to produce a screenshot with transparency. Introduction blog post.

How to use:

1. Click the capture button and share your entire screen. A 5-second countdown will start.
2. Place the windows you want to capture over the webpage’s gray canvas.
3. alphashot will capture 2 screenshots and show you the combined image.