libxmp is a library that renders module files to PCM data. xmp is a module player for Unix-like systems, based on libxmp, that plays over 90 mainstream and obscure module formats from Amiga, Atari, Acorn, Apple IIgs and PC, including Protracker (MOD), Scream Tracker 3 (S3M), Fast Tracker II (XM) and Impulse Tracker (IT) files.
cdsaext is a library of implementations of data structures and algorithms, such as lists, maps, trees, binary search functions, and similar dsa's.
See also my javadsaext project, which implements similar functions in Java.
Cross-platform C++ libraries with a network/internet focus.
NOTE: Current source code as well as bugs/patches are on GitHub:
https://github.com/pocoproject/poco/
C++ class libraries for network-centric, portable applications, integrated perfectly with the C++ Standard Library. Includes network protocols (Sockets, HTTP, FTP, SMTP, POP3, etc.), SQL database access and XML parsing. Licensed under Boost license.