Jellyfish is a tool for fast, memory-efficient counting of k-mers in DNA.
A k-mer is a substring of length k, and counting the occurrences of all such
substrings is a central step in many analyses of DNA sequence. JELLYFISH can
count k-mers quickly by using an efficient encoding of a hash table and by
exploiting the "compare-and-swap" CPU instruction to increase parallelism.

WWW: http://www.genome.umd.edu/jellyfish.html