FreeBASIC is an open source (under GPL), 32-bit, BASIC programming language compiler. It is designed to be syntax compatible with QuickBASIC, while expanding on the language and capabilities. It compiles for DOS, Microsoft Windows and Linux, and is being ported to other platforms.
FreeBASIC makes use of the GNU binutils programming tools as back-end and can produce console and GUI executables, besides dynamic and static libraries.
Currently, software libraries like Gtk, GSL, SDL, Allegro, Lua and OpenGL can be used directly, and more are being added on every new release.
While yet in beta stage, FreeBASIC can already be used in real applications. The compiler, and its more than 45 thousands of lines of code, is compiled by itself. (FreeBASIC is a self-hosting compiler).