Michael Feathers wrote a blog about Open-Closed Principle, where he described simple technique that measures the closure of the code. I created a Groovy script which implements this algorithm for Git repositories. If you run it from the root of your Git project, it produces a CSV file with the statistics of how many times the files have been modified.

As an example, here is the top 10 files from rabbitmq-server repository

845  src/rabbit_amqqueue_process.erl
711  src/rabbit_channel.erl
650  src/rabbit_tests.erl
588  src/rabbit_variable_queue.erl
457  src/rabbit_amqqueue.erl
448  src/rabbit_mnesia.erl
405  src/rabbit.erl