Blogger-atom is a project mainly written in Ruby, it's free.
get blog's feed
HTTP Get Request to the blog's feed
Example
# $ ./run-blogger-atom.rb -f 2010-01.xml -min 2010/01/01 -max 2010/01/31
http://midorex.blogspot.com/feeds/posts/default?published-min=2009-12-31T23:59:00&published-max=2010-02-01T00:00:00
$ ./run-blogger-atom.rb -f label-essay.xml -label essay