PeptidAce is an open source C# library that includes a lot of tools for peptide spectrum matching. It was based on the Morpheus open source project, with the ultimate aim of improving no-enzyme in silico digestion of huge, unannotated transcriptome databases. It excels at identifying non tryptic peptides and can identify peptides with non-standard fragmentation patterns. It can also be used for deep spectrum annotation, matching peaks to all types of fragments and modifications.