Khmer-ngram is a project mainly written in PYTHON and PERL, it's free.
Simple probabilistic de Bruijn graph representation
Code from my PyCon 2011 talk on building ASCII de Bruijn graphs on top of a Bloom filter.
See: http://www.slideshare.net/c.titus.brown/pycon-2011-talk-ngram-assembly-with-bloom-filters
--titus Mar 13, 2011