Kraken is a system for assigning taxonomic labels to short DNA
sequences, usually obtained through metagenomic studies. Previous
attempts by other bioinformatics software to accomplish this task have
often used sequence alignment or machine learning techniques that were
quite slow, leading to the development of less sensitive but much faster
abundance estimation programs. Kraken aims to achieve high sensitivity
and high speed by utilizing exact alignments of k-mers and a novel
classification algorithm.

In its fastest mode of operation, for a simulated metagenome of 100 bp
reads, Kraken processed over 4 million reads per minute on a single
core, over 900 times faster than Megablast and over 11 times faster than
the abundance estimation program MetaPhlAn. Kraken's accuracy is
comparable with Megablast, with slightly lower sensitivity and very high
precision.

REFERENCE
Wood DE, Salzberg SL
Kraken: ultrafast metagenomic sequence classification using exact
alignments.
Genome Biology 2014, 15:R46.