Indigo is an open source software toolkit for chemoinformatics. It is available for Windows, Linux, Solaris, and Mac OS X. It is distributed under the GNU GPLv3. Components of the toolkit * Bingo: Cartridge for Oracle database supporting different kinds of searches in organic chemistry databases * Dingo: Molecule and reaction rendering library * Cano: Canonical SMILES computation library * Deco: R-Group deconvolution and scaffold detection library * Nucleo: Nucleotide chain handling library Major features Format support * Molfile 2000/3000 and SMILES for molecules * Rxnfile and reaction SMILES for reactions * SDF and RDF for collections of molecules and reactions * Rendering library supports PNG, SVG, and EMF Chemistry * Molecule and reaction fingerprinting * Substructure matching (subgraph isomorphism) * Affine transformation matching (Kabsch Alignment) * Chemical conformation matching * Support of cis-trans isomers and chiral centers * Aromaticity perception, aromaticity matching, de-aromatizaion * Tautomer (sub)structure matching * Resonance (sub)structure matching * Molecule similarity search * Canonical SMILES builder (with stereochemistry support) * 2D molecule and reaction layout * Maximum common substructure (MCS) of two structures * Exact MCS of an arbitrary amount of structures * Reaction substructure matcher * Reaction atom-to-atom mapping (AAM) Source code and API * All source code is portable and thread-safe * C interface for selected components * and Java wrappers for selected components * A number of command-line utilities are available