The plainchant of the Ruthenians; according to the wiki entry, it is closely related to Znamenny chant. I've heard some Znamenny; the two forms of plainchant don't sound that similar. Maybe it's because the Znamenny I've heard primarily comes from Valaam, and I haven't really heard pure Znamenny. (Or is it because it's an all-male group?)
Paschal Ode 1 - Prostopinije
Palm Sunday Vespers 2011
Valaam - this example seems to be more like a mix of Byzantine and Znamenny - Valaam chant?
The Znamenny Chant of the Russian Church--Part I; Part 2 [alt]
Church of the Nativity page
Znamenny Chant by Fr. Simon Pimen Pt.1 (Parts 2 and 3)