[ivansavz]

I have two recommendations that I don't see mentioned by anyone else yet:

1. An Introduction to Mathematics by Alfred North Whitehead, 1911 available at http://www.gutenberg.org/ebooks/41568

It not specifically about history, but I found it nice how it builds up concepts from first principles, e.g. "We had problem X, so we invented math concept Y to help with problem X, and then extended the idea concept Z that handles more general class of problems."

2. Mathematics 1001: Absolutely Everything That Matters About Mathematics in 1001 Bite-Sized Explanations Hardcover by Richard Elwes, 2010. (non free)

This one doesn't go into any details on any topics, but it gives you a bird's eye overview of many topics and based on the "sampling" I did for the few concepts that I know, I found the bite-size explanations to be fairly good (i.e. mathematician explains things in plain language, and not science journalist simplistic analogy).