Free eBooks: Spotbit

From Twitter via top_book:

Spotbit: Paperless Publishing Free

This is an odd beast. All the free ebooks are downloadable .exe files (which I guess = PC only). If I understand this correctly, it turns a PDF into a computer program and the PDF file becomes a page-flipping eBook. There's a big variety of free eBooks there. Yet I wonder if all of them are legal.

For instance, is this one legal?