OpenLaszlo is an open source platform for creating zero-install web applications with the user interface capabilities of desktop client software.

OpenLaszlo programs are written in XML and JavaScript and transparently compiled to Flash and, with OpenLaszlo 4, DHTML. The OpenLaszlo APIs provide animation, layout, data binding, server communication, and declarative UI. An OpenLaszlo application can be as short as a single source file, or factored into multiple files that define reusable classes and libraries.

OpenLaszlo is "write once, run everywhere." An OpenLaszlo application developed on one machine will run on all leading Web browsers on all leading desktop operating systems.