For creating YouTube videos similar to Your Youniverse and YouAreCreator, there are several great free tools you can use. Here are a few recommendations:

DaVinci Resolve: This is a professional-grade video editing software available for free. It offers a wide range of features, including easy transitions, audio editing, and on-screen text.

HitFilm Express: Another powerful free video editor that includes various effects and transitions. It's user-friendly and suitable for both beginners and advanced users.

Shotcut: A free, open-source video editor that supports a wide range of formats and provides numerous features for video editing, including transitions and text overlays.

Lightworks: A professional video editing software with a free version that includes essential features for creating high-quality videos.

For easy transitions between images, adding your voice, and displaying transcription on the screen, these tools should be more than sufficient.

Additionally, if you’re interested in learning more about video editing and possibly developing your own video editing app in the future, you might find this blog useful: https://www.cleveroad.com/blog/how-to-make-a-video-editing-app/. It offers a comprehensive guide on the process and might provide you with some valuable insights.

Good luck with your YouTube channel!