MobClock is a project mainly written in Java, it's free.
Mobile clock showing current moon phase and a weather forecast. Deployed on MIDP/JavaME (wallpaper option on Sony Ericsson phone).
Copyright (2010) by Marius Mikučionis
License
GPL version 2.0
Requirements
It should be possible to run in a stand-alone mode on any JavaME-capable phone, but some Sony Ericsson phones have a neat feature of setting JavaME application as a wallpaper. I assume the following configuration:
Device configuration: CLDC-1.1 Device profile: MIDP-2.0 Screen resolution: 240x320 (it is possible to change the images inside jar and thus fit the app for other resolutions without changing the code, feel free to hack it) A phone that supports SEMC-StandbyApplication: Y (some Sony Ericsson model), look for "Application" option for Wallpaper setting (see Settings->Display->Wallpaper). The application does not require any special access or permissions, it is self-contained and uses CPU for drawing the screen only upon request (it is completely passive when not showing).