Is there an equivalent to the Mac OS X software Hazel?
I use maid : http://alternativeto.net/software/maid/ Love it, keeps everything as clean as if I had a, well, maid!
You can install Maid in Ubuntu as follows:
sudo apt-get update; sudo apt-get install -y ruby1.9.1 rubygems; sudo gem install maid
For more info (such as how to write rules), look at the projects README.