Lately Syncfusion started producing e-books grouped under Succinctly series. The books are for developers on (mostly) Microsoft platform and are a free download albeit registration is required. I’ve peeked into few of them and I have to say I like them.
They won’t replace commercial n-hundred pages long developer books though but they provide you an introduction, the basics of the topic and serve as quick reference. So it is worth checking them out and kudos to Syncfusion.