This is MeRIT, the Mensural Rhythm Interpretation Tool, is a client-side Javascript tool that interprets the rhythmic notation of pre-modern polyphonic music using rules derived from the writings of the fifteenth-century music theorist and composer Johannes Tinctoris (c.1435–1511).
MeRIT can be used through the MeRIT website: interpreter.earlymusictheory.org
For rendering, MeRIT is using Verovio, an open-source library developed by the RISM Digital Center with the support of the Swiss National Science Foundation.
MeRIT is an output of the AHRC-funded research project Interpreting the Mensural Notation of Music (2017–2022) [grant number AH/P013910/1], an hosted at the Royal Birmingham Conservatoire. For more information about the project and its team, funding, and outputs, please see the ‘about’ menu on the MeRIT website.