Thanks to a very generous donation, the entire set of (seven or eight) volumes of the Nova Organi Harmonia will be made available for free download on the CMAA website very soon. I have three volumes myself that I purchased awhile back from a German bookseller. The entire set is almost impossible to find these days.
The main reason this would be of interest would be for those who like accompanied chant (organ accompaniment). With this set of volumes, very nice settings of the organ accompaniment will be available for virtually all propers for the liturgical church year.
That being said, I personally prefer the chant to be sung without accompaniment, which I believe to be ideal. Plus, without a very well-trained organist (and one who is especially well-versed in how the chant is sung), trying to use accompaniment can be disastrous. But... for those who are in the know about organ accompaniment of the chant, this is the best arrangement out there. It is amazing that it is now to be made available for free TO THE WORLD at the CMAA website. Check out the samples that are available now: http://chabanelpsalms.org/introductory_material/NOH_ex.htm
Please consider making a donation to support this and other worthy projects to the Church Music Association here. To donate to the Chabanel Psalm project, you can make an easy donation (even small amounts are helpful) here.