Aranha (pronounced aranya) is a simple web spider written in python using gevent for asynchronicity. Aranha means "spider" in portuguese.
Aranha's goal is to be suitable for projects that need light url fetching or a simple spidering of a few classes of webpages. If spidering is a major part of your project, you probably want to either write your own spider or use scrapy as a base, as it's much more sophisticated.