One originality of this development is that it was user-funded, and I proudly participated one year ago, donating a (tiny) amount of money.
I believe notmac is great, but only for those users having a spare mac to backup on, which is not so general...
I would have much preferred the server side to be some php-based script that one would simply upload on your average, ISP-provided webserver.
Now, Notmac is here, and would it be just through the way it was invented and paid for, it's worth remembering.
(all the more as my younger son will soon replace his mac mini ;-)