Hi! I just released Caption Tool, a simple tool for adding image and sound captions to your Ren'Py game. (For an example of a game using this tool, take a look at last day of spring.) It was made in Ren'Py 7.2.2.491.

Features:

• Image captions that work with Ren'Py's self-voicing option
• Sound captions for describing music and sound effects
• Dialogue on first run asking if users want to turn on captions
• Button to Ren'Py's built-in accessibility menu, which has options to change the font, font size and line spacing
• Guide to show how these functions work in-game

I've tried to make the tool as straightforward as possible, with an in-game guide explaining each function with examples of how to use it, so that people can easily add captioning to their own Ren'Py games. 

If you run into any issues or have any questions, please let me know!