I recently found a great site/app to help you develop your story. And it's called BEEMGEE.

BEEMGEE allows you to create a character by asking you a list of questions based on the characters involvement in the story, instead of focusing on what the character looks like. This way you will completely understand your character and you might even get a new idea for the plot, like I did.

Once you have filled in the questions, you can compare all of your characters' profiles to each other and make an overview of all the differences between your characters. Maybe you can find some areas your characters might butt heads on and use that to add to the story's conflict.

There is also an option to plan out your story with little events cards. These cards inlcude who is present in the scene, where the scene takes place, whether it is a central storyline, a flashback or a prologue, and the description of what happens during the scene. The biggest plus of this is that you can manage these cards by just dragging them if you decide one of the events has to take place earlier or later, and still have a clear overview.

Once you have done this, you can go to the step outline where all of you events together form a synopsis of your story and basically show you whether there are no big jumps in the storyline or whether it flows nice.

And these are just the main tools of the free version! The premium version helps you go even more in depth with the characters and the storyline. Also, people can submit requests in what they would like to see added to the author tools, and they are always updating.

An explanation of all the features that the author tool has, and will get, are explained here: https://www.beemgee.com/feature-roadmap/

If you want to try it out, here's the link to the app itself:
https://www.beemgee.com/app/