From publisher blurb:
A newly discovered spell allows wizards to liberate their familiars as a reward for all their hard work over the years. These tiny beasts with magical spirits are now able to adventure side-by-side with the other races, equally! This book contains everything you need to play D&D as a former familiar.
All the familiar species are included and balanced for exciting gameplay. Thirteen animal races from the Find Familiar spell are available to you and each has three distinct sub-races. That is nearly 40 animals you can choose from!
Your familiar can choose from 6 classes, each of which leans heavily upon one of the six abilities. Within each class are three sub-classes. These draw from the three aspects of every familiar: their physical form, their arcane past, and their spirit type (Celestial, Fey, or Fiend). The book also contains rule options for those who want to play existing classes.
Wizards rely on their familiars in different ways. UnFamiliar offers 13 distinctly different backgrounds to reflect your past experience. As part of the balancing with the standard races, each background includes a new cantrip you can cast. This cantrip was not only helpful for your previous life as a familiar but will be useful for adventuring, too.