OS X has a "Quick Look" feature which enables quickly previewing any file by tapping the space bar within the Mac's finder. QuickLook is an open-source application which aims to bring the same functionality to Windows.

To use the program, simply open Explorer, browse to a file and hit the space bar. The program opens a preview window to display images, videos, archives, PDFs, markdown files, HTML documents, text files, Office documents if you have Office installed, and more.

Once the preview window is visible, you're able to use the up, down, left and right arrows to preview another file, or hold down Ctrl and spin the mouse wheel to zoom in and out.

A plugin interface enables other developers to expand QuickLooks viewing capabilities.

0.2.5:

Fix the instability when previewing video and audios, which was introduced in version 0.2.4.
#50: Window moved unexpectedly when size is small.
#55: Incorrect plural words: "files" and "folders" when there is only one of which.

Verdict

QuickLook is very new, and has plenty of bugs and issues. We tried previewing a GIF, for instance, and although it opened correctly, just dragging the window around seemed to cause the program to do some processing, until eventually it crashed.

On the plus side, the program worked most of the time, problem-solving updates are appearing every few days, and as QuickLook doesn't requre installation, you can try it without any risk.

Overall, if you're interested in the idea, give QuickLook a try-- but don't expect stability, just yet.