I dunno how many real world web apps can get by with the power of a micro-instance, but if you're the author of a weakly Windows web application, you can now run it on the Amazon cloud for free for a whole year.
750 hours of Amazon EC2 Microsoft Windows Server Micro Instance usage (613 MB of memory and 32-bit and 64-bit platform support) – enough hours to run continuously each month*
Otherwise free tier micro instances are good for running multi-user git servers and other peripheral team servers with low traffic / power needs. It's cheaper than paying github monthly for private repositories and team workflow tools.