OpenTiles is an open source (licensed under GNU GPL) sliding tile game in which the goal is to align the numbers 1 to 15 in the correct order. It is a simple puzzle game with no complicated rules, a simple interface and small size (both in terms of screen space and filesize). It is coded in Visual Basic 6. The latest stable release (as of 10 July 2007) is version 2.0
NOTE that this project hasn't been updated in a very long time
OpenTiles is being developed on 32-bit Windows XP and Windows 2000 systems and thusfar tested only on these platforms. It should be able to run under Windows 95/98/Me because it doesn't have many external dependencies (no graphics/sound/math/etc. libraries or DLL's required, apart from the VB6 runtime) and only uses the native Windows graphics procedures for lines and text. Because OpenTiles is coded in Visual Basic it cannot be natively run under or compiled for operating systems other than Windows, but it will probably work under WINE on Unix/Linux (though this is not tested yet; please email Hannes (via user's page on SF) if you ran OpenTiles successfully on platforms other than 32-bit Win2K/XP with info on the system used).
As of July 2007, OpenTiles is being developed by Martin and Hannes.