AlertPOP is described as '! - Add non-intrusive popup messaging to you application'. There are three alternatives to AlertPOP for Windows. The best alternative is Snarl, which is both free and Open Source. Other great apps like AlertPOP are FP-QUI (Free, Open Source) and MessagePop (Free).
FP-Notifier has been renamed to FP-QUI. FP-QUI generates popup-windows that provide users a quick and ubiquitous interface to practically any application that supports command line instructions or named pipes.