As the front page to which I linked above describes, this is a project to put recordings of the whole Graduale on YouTube. When completed, this will be a superb resource for Scholas (or Scholae?) and for anyone else interested in the musical patrimony of the Church.
The videos often show the early (pre-square-note) notation of neumes which is fascinating for those wanting to learn how to use the Graduale Triplex.
Here is the first video they posted (there are already many more):