There are plenty of C/C++ libraries that you can use to make 2D games. I came across allegro from one game development forums. Allegro games run on multiple operating systems and there is no restriction of modern hardware. Allegro can run on older operating systems like BeOS, DOS and other older graphic rich OS. If you’re looking for any C/C++ library to develop your 2D game then take a look at allegro.
Those who use SDL or similar other C/C++ library will find allegro easy to use like SDL but much more feature rich than SDL. Allegro API is improved a lot and now because of that you can do both low and high level functions using this library. It also supports 3D and there are some demos available for you to view 3D capability of this library. Just like SDL it also handles threads,timers,sound,networking,player input, etc,in addition to all that, Allegro also has GUI support just like Irrlicht does. Don’t expect this library to be like irrlicht though as it is more suitable for 2D than 3D games.
Allegro Games in BeOS
Allegro has flexible license for developers and there are no strict restrictions for using it. License can be classified into “giftware” category, so that allows you to even distribute the games under commercial license.
You can get more information about it from Allegro website.