Is there a way (I think only needed / possible for desktop versions) to add multiple task at once.
For example a tekst box where each line is a task which will added to the "current" project or the possibility to at some keyword wich let ToDoIST organize it. A kind of Rapid entry?
Yes, that is indeed possible. To do so, please click on the name of the project on the left side and when you're in the project, use the "Add task" link at the bottom. This way, each time you hit Enter the task will be saved and another input box will open so you can quickly add and save tasks one after another.