Library to create high-performance server applications

Answer 1

Perhaps ACE?

Answer 2

Spserver uses libevent and so should have good performance on all platforms.

You could use Boost.ASIO directly and thread pool:

Multiple threads may call io_service::run() to set up a pool of threads from which completion handlers may be invoked ... all threads that have joined an io_service's pool are considered equivalent, and the io_service may distribute work across them in an arbitrary fashion.

Answer 3

POCO? libevent? Got any further clues?

Answer 4

Qt?