I´m going to develop a windows desktop application with JavaFX. In order to promote my ideas about the design, I want to build a prototype (no code, just UI). Can someone recomend a software for this, besides MS PowerPoint.
Take a look at Adobe XD. It is a drag-n-drop prototyping application. It is intended for designers that have little or no programming experience, and it really is amazing how powerful it is for creating a professional prototype.
Adobe offers XD for free, so you can download it and do the tutorial. You'll see how easy it is to make something impressive in ten minutes.
I have posted this before and the OP loved XD.
I have had good success using Balsamiq. Balsamiq lets you drag and drop components to create a wire-frame UI that does not look like a finished product. This can be helpful when showing the UI to clients (and bosses) who typically think that the product is the UI and if the UI is done then the product is almost done even though none of the functional code has been written. Balsamiq creates a UI that looks like a prototype to avoid the above problem. It also allows clicks on items to bring up other UI forms so you get an interactive prototype.