Twproject offers an interesting functionality to export and import projects in Json Format. This functionality is very useful in case you have to migrate partial data, or you want to bring in your production environment some test projects created during the trial period.
This functionality is available both, in the projects list page, and in the single project page.
You can find it by clicking on the arrow button at the top right of the page. 
This export include the project structure with all project sk details and assignments.
The export do not includes project costs, ToDos, worklogs and documents.
The exported file can be imported from the same button in a different Twproject instance.