DHIS2 uses Launchpad as the main collaboration platform. The site can be accessed at http://lanchpad.net/dhis2 Launchpad is used for source code hosting, functionality specifications, bug tracking and notifications. The Bazaar version control system is tightly integrated with Launchpad and is required for checking out the source code.
The various source code branches including trunk and release branches can be browsed at http://code.launchpad.net/dhis2
If you want to suggest new functionality to be implemented in DHIS2 you can air your views on the developer mailing list and eventually write a specification, which is referred to as blueprints in Launchpad. The bueprint will be considered by the core development team and if accepted be assigned a developer, approver and release version. Blueprints can be browsed and added at http://blueprints.launchpad.net/dhis2
If you find a bug in DHIS2 you can report it at Launchpad by navigating to http://bugs.launchpad.net/dhis2 Your bug report will be investigated by the developer team and be given a status. If valid it will also be assigned to a developer and approver and eventually be fixed. Note that bugfixes are incorporated into the trunk and latest release branch - so more testing and feedback to the developer teams leads to higher quality of your software.