External plugins or extensions can easily be developed for OSGi.fx. Since OSGi.fx has itself been developed using OSGi and Eclipse e4, you can easily leverage their modular capabilities to build your own extensions.
Please have a look at how the bundles with com.osgifx.console.ui.* project name pattern are developed.
[!TIP] As a starting point, refer to the sample Tic-Tac-Toe Extension.
Once the extension is developed, you can test it by installing it from the Actions -> Install Extension menu option.
To develop an extension, you need to provide an OSGi Deployment Package archive.
For ease of development, you can use the OSGi.fx workspace to further develop your own extensions. The workspace comprises a new bnd plugin which will enable you to automatically generate a deployment package from a bndrun file.