Compilation

C# (.NET / Mono): Compiled to CIL

csc source1.cs source2.cs /out:program.exe
gmcs source1.cs source2.cs -out:program.exe

Vala: compiled to native code via C code as intermediate code

valac source1.vala source2.vala -o program

Vala's standard object system is GObject, compiled Vala libraries are valid C libraries.

Using Packages

Mono: -pkg:

gmcs source.cs -pkg:gtk-sharp-2.0 -out:program.exe

Vala: --pkg

valac source.vala --pkg gtk+-2.0 -o program