The Mishna & later rabbinic collections & commentaries on oral Torah [talmudim & tosefta] are arranged in six general "orders" [sedarim], each of which contains several named tractates [massektoth] reporting tannaitic traditions vaguely related to a central theme. The bulk of the traditions recorded in the Mishna have to do with rules of behavior [halakah]. But these are frequently interspersed with other types of sayings, anecdotes & traditional lore ['aggada].
The only tractate in the Mishna that is devoted entirely to transmitting non-legal opinions is Pirqe Aboth ["Sayings of the Fathers"], which catalogs the wisdom sayings of rabbinic sages, including several of the 2nd temple period. Aboth was probably composed before & originally published independently of the Mishna, since it does not fit well in its current location in Neziqin, the order of tractates concerned with civil & criminal law.