PockeTwit is a twitter client for the Windows Mobile Professional platform.

Features:

A unique user interface
Works on VGA, QVGA and SmartPhone devices
Support for multiple twitter and identi.ca accounts
Maps view shows users on a world map and allows searching by region
“Conversation View” shows a what this status was in reply to.
Uses standard notifications to alert you of new friends statuses or replies
URL shortening with is.gd
Integration with shorttext.com for tweets longer than 140 characters
Take photos and send to TwitPic
Integrated search.twitter.com
Clickable @names, URLs, and #Hashtags
Option to check for new version on startup
Themes

http://code.google.com/p/pocketwit/

Cards is an application for learning by heart efficiently all kinds of facts on Windows Mobile devices and/or Windows desktop PCs.

http://code.google.com/p/cards/

Sipek Mobile is an open source mobile SIP client project for Windows Mobile based devices. The application is based on SipekSdk and consequently pjsip.org SIP stack. In other words it’s a mobile version of Sipek Softphone.

http://code.google.com/p/sipekmobile/

Mobile Storage with encrypt for Windows Mobile 6.0 and higher Based on .NETCF 3.5.

http://code.google.com/p/mobilestorage/

Calk is a very simple calculator for .NET 2.0 enabled mobile devices with 240×240 pixels display!

http://code.google.com/p/calk/

AntiTheft (Car Alarm) and TRACKer using mobile and GPS – export in KML – Remote Control. For S60 3rd and 2nd edition phones!

http://code.google.com/p/attrack/

Web Service project for Symbian OS S60 3rd Edition.

http://code.google.com/p/terraws/

The Ensymble developer utilities for Symbian OS is a collection of Python modules and command line programs for Symbian OS software development.

Current focus of Ensymble development is to provide useful tools for making Python for S60 (PyS60) programs. A long term goal of Ensymble is to provide a cross-platform, open-source way to do Symbian OS software development, supporting Symbian OS versions 9.1 and later.

SIS files made with Ensymble work from S60 3rd Edition phones onwards. For 1st and 2nd Edition phones there’s py2sisng.

http://code.google.com/p/ensymble/

OpenDocument Reader for Symbian OS.

http://code.google.com/p/officereader/

Cairo for Symbian OS is based on Cairo version 1.8.6 with new surface backend added to allow Cairo rendering to a Symbian OS window.

http://code.google.com/p/cairo-for-symbian/