The Sodium crypto library
download.libsodium.org
download.libsodium.org
For something new, you may want to look at its little brother instead: https://github.com/jedisct1/libhydrogen/wiki
Anyway, version 1.0.12 will be released soon.
Also, thanks for not ignoring Windows.
It was designed to provide high-level APIs to perform common operations, abstracting implementation details. And this is what it gets optimized for. The Hydrogen API which libsodium 2.0 will be based on makes this even more obvious.
Low-level primitives are available (or partially available, in minimal builds) only to provide backward compatibility with NaCl, or because the final construction hasn't been chosen yet.
That said, SHA-2 is about 20% faster in version 1.0.12 while remaining portable.
Fun fact, sha256 in openssl pulls in asn1 parsing even after section garbage collection. Yup.