KDE is a friendly community which hosts hundreds of projects. Any project which follows the KDE manifesto and KDE Vision is welcome to join us.

The term "application" is used here to mean any project hosted in KDE Git and includes programming libraries and development tools but not typically infrastructure tools or projects with other end product outputs.

playground

playground is a Git module for projects starting development

You will need a Git write account which needs a referral from another KDE contributor, see Get_a_Developer_Account
You will need to to ask sysadmin to create a module
Projects can start in scratch repos without asking for a repo, see Git KDE.org manual
Projects can make alpha releases and can put them on download.kde.org unstable
Projects can ask for translations for their master branch only

Incubator

Projects which started life outside of KDE are welcome to join us if you feel our community makes a good fit through the KDE Incubator.

The projects should follow the KDE Incubator process.
A sponsor will guide you through the process and check your project complies with the needs of the KDE community

kdereview

Projects move into kdereview when they are ready to start making beta or stable releases. It allows for the KDE community to check over for minimum standards.

You can move your project in repo-metadata, see repo-metadata README or file a Sysadmin ticket asking for the move
See the Sanity Checklist for some of the elements people will review
E-mail kde-core-devel and other relevant mailing lists with details of your project
Make fixes to issues people bring up
Wait at least two weeks in kdereview