Things_db_parser is a project mainly written in Ruby, it's free.
Some ruby to parse the Things Database.xml file
A script to parse the Things Database.xml file and list the tasks for a particular project
ruby things.rb PROJECT_NAME PATH_TO_DATABASE
e.g
ruby things.rb "My Big Project" "/Users/wal/Library/Application Support/Cultured Code/Things/database.xml"
or just ruby things.rb "My Big Project"
if your things database is in the standard location ~/Library/Application Support/Cultured Code/Things/database.xml