An abstract shape is a mathematically well defined coarse grained view of an RNA structure, supporting the user to focus only on "interesting" structural features.
RNAshapes and pKiss operate on single sequence inputs. Their counterparts RNAalishapes and pAliKiss take an multiple sequence alignment as input. RNAshapes and RNAalishapes predict purely nested secondary structures. pKiss and pAliKiss additionally consider H-type pseudoknots and kissing hairpins.