Tamora Pierce is best-known for her YA fantasy novels set in the land of Tortall, and all but two of these stories (the other two being modern-day tales) take place there. Fans of hers will devour this in a snap, but you don't have to be familiar with her work to enjoy them.
For this review, though, we're operating on the assumption you're familiar with Pierce's work. The majority of the stories are, for the reader, going to be great fun--the backstory (or side story) that you didn't you you wanted.
Student of Ostriches Although the book won't tell you, this is the story of the Shang Unicorn mentioned in the Lioness quartet (a famed and powerful martial artist). Kylaia al Jmaa isn't pretty, like her sisters, but when she's out with her herd, she learns from the animals around her how to defend herself.
Elder Brother When a mage is turned into an apple tree (Immortals quartet), an apple tree half the world away turns into a man, and has to deal with the strange world he now lives in.
The Hidden Girl Set in the same country as Elder Brother, the story of a girl who must live within the society's strict religious rules. A thinly-veiled commentary predominantly on Islam (although Pierce's end notes mention Judaism and Christianity as well) and extremism.
Nawat The story of Aly's first children, and how Nawat Crow deals with having children (Trickster series). One of the weaker stories, because Nawat can be unbearably thick at times, and it probably doesn't make as much sense as it *should* unless you're familiar with the backstory of the crows, the Copper Isles, and everything else.
The Dragon's Tale A 15-year-old Kitten (a.k.a Skysong, Immortals quartet) and what she gets up to when her foster parents are distracted. Hey, it's not *her* fault the silly humans think she's a lizard and don't believe that she's more intelligent than they are...One of the best stories, and easily understandable without knowledge of the series.
Adria Not related to any of the series, a young mathematics genius learns about the outside world. Short, sweet, and more filler than anything else.
Plain Magic A girl loses a lethal lottery, but all is not as it seems. The first short story Pierce wrote, which you can tell when you try to figure out why the dragon in this story is much different than the established, intelligent and curious dragons of canon. Still, it's actually very good and makes you want a continuation.
Mimic In an undisclosed valley, a girl finds a curious lizard nearly dead, and nurses it back to health. Again, short but makes you want more.
Huntress A modern story set in New York. Corey is accepted to the elite Christopher Academy and its track team, but discovers a vicious secret. Also a fairly weak story.
Testing At the Smithton Home for Girls, every new housemother has to go through the girls' rigorous testing before being accepted...and no one's made it through yet. Based on Pierce's experiences as a housemother.