Bulletin of the American Mathematical Society, Electronic Journal of Combinatorics, Electronic Journal of Physics, some more obscure ones like Forma, are free to access at once... There are very many open access journals in the maths. Most do not implement commenting however unlike your example (which is quite recent).
PNAS (quickly publishes) and Complex Systems are two journals semiopen. After a year or quarter year the content becomes available to everyone free.
Please clarify what you mean, because there are a very large number of quality open access, if not entirely open (with commenting journals), as I'm sure you know. I can include some less well known ones that are high quality if that is the question?
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