It is the last tractate in the order, because of its shortness (3 chapters) and because it deals with a very rare and unusual area of Jewish law.
The premise of the tractate is the obligatory bird-offering that has to be brought by certain people (for instance Nazirites at the completion of their vow and women after childbirth).
However, the Mishnayot of the tractate are included in the Daf Yomi cycle, and are printed in the standard editions of the Talmud.
Kinnim is considered to be one of the most difficult tractates in the whole Talmud, largely because the mishnayot involve rather elaborate counting methods and practices.
[2] These resemble certain forms of counting found in discrete mathematics and, appropriately, make use of the pigeonhole principle.