By Elizabeth E. Wein.
The Winter Prince is a good (though it seems a little short) take on Arthurian legend, from the viewpoint of Medraut (Mordred). It may have a bit too much angst about his relationship with his mother, but I thought it was well done. You may think I'm biased towards Arthur stories because I also enjoyed Jo Walton's The King's Peace and The King's Name, but it isn't so. (He doth protest too much, right? Better take this with a grain of salt.) I read another Arthurian book recently that I thought was pretty bad. (I am not planning to write a review of it, since I didn't finish it.)
A Coalition of Lions takes Wein's series into original territory. After the disaster at Camelot, the king and his sons are dead. His only daughter, Princess Goewin, travels to Aksum (ancient Ethiopia) to marry her betrothed and reclaim her kingdom from her aunt Morgause. She doesn't find what she expects, though.
In the third book, The Sunbird, she sends her young nephew Telemakos to spy out who is breaking the trade embargo in Aksum and spreading plague.
While all three are shelved as young adult, they do contain violence and cruelty. Wein's heros and heroine are not invincible or even superhuman; they suffer. There is no obvious magic*; these books ring of historical authenticity. (I suspect Wein has done her research well.) Both Aksum and England are Christian countries, but not everyone is well educated. (Medraut describes a scene with his siblings where they fail to recognize a scene from Revelation and says "Don't you even know what you believe in?")
Flaws are perhaps that they seem a little short, especially The Winter Prince. In A Coalition of Lions the great conflict is resolved too easily. Telemakos falters when presented with an opportunity for revenge at the end of his travail.
Still, I enjoyed them quite a bit and recommend them. I'm looking forward to reading The Mark of Solomon, featuring the further adventures of Telemakos, after the second book comes out next year.
* (The one possible exception is that Medraut, whose name means "Marksman", always hits what he aims at. I am labeling them fantasy because that's what Arthurian legend is usually considered.)
Update: Two minor notes. I think I found this book because it was mentioned here, and I also just found the author's LiveJournal.