ImpLib SDK is intended for authoring custom MS-COFF Import Libraries with advanced features, like cdecl2stdcall thunks, importing by ordinal, removing original thunks and others. There are many nonstandard situations, like interfacing a CDECL DLL from Visual Basic 6, prototyping a set of DLL functions for PureBasic, mangling the symbolic aliases for an existing object file in Visual C/MASM32/NASM and so on. ImpLib is just a set of tools, which might help you solving this kind of problems. It is not required to know the internal structure if an Import Library file. Read the [Guide] for a more detailed description and a set of usage tutorials.
ImpLib is free even for commercial use and redistribution of any kind, as long as all copyrights are preserved. The whole package is provided "AS IS". Check the license file included in the current release for additional info.
PureBasic OpenAL SDK is hosted here as well. It was built using ImpLib.