ClanLib is a cross platform C++ framework. Essentially the library offers a series of different functionality under a streamlined API. Its primary focus is on games, although its not limited for that usage only.

Rough Overview of ClanLib Functionality
Supports Microsoft Windows, Linux and Mac OS X
Basic cross platform runtime (threading, file I/O, etc.)
Template based C++ signal library (type-safe callbacks / delegates)
Integrated resource management
Sound mixer supporting wav, mikmod formats (mod/s3m/xm/..), ogg vorbis
XML/DOM support
High-level 2D graphics API supporting OpenGL and SDL as render targets
Batch rendering engine giving maximum performance when rendering 2D with OpenGL
2D collision detection
2D sprite animation support
Highly customizable GUI framework
Network library with low-level to high-level interfaces
Cross platform OpenGL 2.0 wrapper (target Microsoft Windows, Linux and Mac OS X at the same time)
Full reference manual and many overviews which goes in detail on various topics in clanlib
Framework libraries generally support the same things that can be gained by combining other specialized libraries. However, a good framework will combine and simplify the usage through a common set of conventions. The primary goal of ClanLib is to aid developers to rapidly create games and other applications.