About 10,000 hours (on the calendar, not of work!) after its first public release, the Vcsn team is very happy to announce the release of Vcsn 2.1! Vcsn is a platform for weighted automata and rational expressions. It consists of an efficient C++ generic library, shell tools, Python bindings, and a graphical interactive environment on top of IPython. It is quite hard to cherry-pick a few new features that have been added in Vcsn 2.1, as shown by the 4k+ lines in the NEWS file since 2.0. For details, see http://vcsn.lrde.epita.fr/Vcsn2.1. However, here are a few headlines: - Many pages of documentation and examples have been written (see http://vcsn.lrde.epita.fr/dload/2.1/notebooks). - Now http://vcsn-sandbox.lrde.epita.fr/ provides a live demo. - Packages for popular distributions (including for Docker) are already available to simplify the installation. - Transducers are much better supported, with improved syntax and several algorithms (e.g., letterize, synchronize, partial_identity, is_functional, etc.) - Expressions now offer several sets of identities specifying how they should be normalized. More generally, input/output of expressions have been improved to match most users' expectations. New operators are accepted: `&` for conjunction, `:` for shuffle, `&:` for infiltration, `{c}` (postfix) for complement, and `<+` for deterministic choice. - When entering an automaton (e.g., with `%%automaton` in IPython) user state names are preserved. - Of course, many bugs were fixed, many algorithms were sped up, and internal details have been cleaned up. - As Easter eggs, many features have also been added, but not advertised, until we are sure of how we want them to look like. People who worked on this release: - Akim Demaille - Antoine Pietri - Canh Luu - Clément Démoulins - Lucien Boilod - Nicolas Barray - Sébastien Piat - Sylvain Lombardy - Valentin Tolmer - Yann Bourgeois--Copigny People who have influenced this release: - Alexandre Duret-Lutz - Jacques Sakarovitch - Luca Saiu To download Vcsn 2.1, and for any information, visit <http://vcsn.lrde.epita.fr/Vcsn2.1>.