how to build a php mysql application that works offline

I have worked with similar system for ships. Internet is expensive in the middle of the ocean so they have local web servers installed with database synchronization via e-mail.

We also have created simple .exe packages so people with no experience can install the system or update system...

There are essentially 3 ways to go:

Version 1: "Old school": PHP-Gtk+ and bcompiler

• first, if you not have done so already, you need to separate your business logic from your presentation layer (HTML, templating engines, ...) and database layer
• then adapt your database layer, so that it can live with an alternative DB (local SQlite comes to mind) and perform synchronisation when online again
• Finally use PHP-Gtk+ to create a new UI and pack all this with bcompiler

Version 2: "Standard": Take your server with you

• Look at Server2Go, WampOnCD and friends to create a "double clickable webserver" (Start at Z-WAMP)
• You still need to adapt your DB layer as in Version 1

Version 3: "Web 2.x": Move application from server to browser

• Move your application logic from the server side (PHP) to the client side (JS)
• Make your server part (PHP) only a data access or sync layer
• Use the HTML5 offline features to replace your data access with local data if you are offline and to resync if online

Which one is best?

This depends on what you have and what you want. If most of your business logic is in PHP, then moving it into the browser might be prohibitingly expensive - be aware, that this also generates a whole new class of security nightmaares. I personally do not recommend porting this way, but I do recommend it for new apps, if the backing DB is not too big.

If you chose to keep your PHP business logic, then the desicion between 1 and 2 is often a quiestion of how much UI does your app have - if it's only a few CRUD forms, 1. might be a good idea - it is definitly the most portable (in the sense of taking it with you). If not, go with 2.