The Little Manual of API Design
From APIDesign
Nice condensed introduction to API design for C++ was written down by Qt developers: troll.no. There is not much new compared to TheAPIBook but some observations are ammusing and I like the little differences and strange similarity of the C world.
The pdf may be nice example that when the time comes, the same things start to independently happen at the different places at the same time. TheAPIBook went to publishing May 4, 2008.