I'm planning to convert some for Windows applications forms from a platform that was discontinued (the converted app will remains for Windows). PHP-GTK seems to be a good choice in that objective since I'm using PHP for internet development and could reuse the same code.
Could you give your impressions about PKP-GTK?
(Just one concern, it's not released since 2008)
Also, I know nothing about this, but it might be worth investigating:
If you can tell us a little more about the nature of the apps you're redeveloping we may be able to suggest some alternatives.