Vala is a new programming language that allows modern programming techniques to be used to write applications that run on the GNOME runtime libraries, particularly GLib and GObject. This platform has long provided a very complete programming environment, with such features as a dynamic type system and assisted memory management.
Before Vala, the only ways to program for the platform were with the machine native C API, which exposes a lot of often unwanted detail, with a high level language that has an attendant virtual machine, such as Python or the Mono C# language, or alternatively, with C++ through a wrapper library.
The GNOME runtime contains GThread ,GIO, GModule, GLib and GObject libraries , and these libraries are crossing platform such as Windows,Linux and other platforms.
The program writed by vala can compiled to C language based GLib library, the can be used by the applications writed by C language.