Sigma (“Simple greedy multiple alignment”) is an alignment program. It's algorithm and scoring scheme are designed specifically for non-coding DNA sequence.

It uses a strategy of seeking the best possible gapless local alignments. This happens at each step making the best possible alignment consistent with existing alignments. It scores the significance of the alignment based on the lengths of the aligned fragments and a background model. These may be supplied or estimated from an auxiliary file of intergenic DNA.