Note: This review addresses v0.4 of the software.
Belvedere is an interesting start at a useful program. At version 0.4, it is clearly just getting started. What has been done, while useful in and of itself, is pretty feature-sparse.
Belvedere, modeled on a Macintosh program called Hazel, allows you to set up simple rules for file management, which the program then executes in the background. For example, it might delete all files in the "Temp" directory that are more than a week old, or sort all your archive files in your Download directory into a sub-folder. While the interface is very basic, and there is no included Help file, it took only a few minutes for me to set up some useful rules.
Some of the features you might expect, but which are not yet present, include regular expressions for file names, the ability to rename files based on a pattern (for example, to add the trailer "_old" to all files more than a week old), or to load and save sets of rules, or reorder rules. However, the existing functionality does cover most likely use cases.
If the current feature set is workable for you, Belvedere might be worth a quick download. This is beta software, though, so you may wish to use it at your own risk and test any rules carefully before letting it run unattended.