BrowserCam has long been the best tool for testing websites in a multitude of situations; however, it isn’t free, so its usefulness is limited for people who just want to test a new design quickly: enter BrowserShots.
This free website has most of the features developers will need to test their sites; however, unlike BrowserCam, there seem to be waits of up to 20 minutes for some OS/Browser combinations, so it is better for casual testing to ensure compatibility rather than live tweaking—it does have a detail page to show how long your wait will be. It has a few useful features: all screenshots are of the entire screen instead of a small part and requests are based on the website, so multiple people can view the results without sharing log-ons.
However, the most interesting part is that the software that runs it is freely distributed and you can, optionally, help the project by volunteering to run a screenshot “factory” from your computer that operates in the background while you go about your normal computing business; thus, combining the best things in life: free stuff and being nice to others. You can just feel the good karma coming.
Besides…it beats signing up for multiple 24-hour previews…