Hi,
I have developed a webapp https://myshmup.com where you can edit or create a vertical shmup (without coding).
The design is inspired by Scratch, you can remix published games for example.
Most of the sprites come from the open game art forum and are licensed under creative commons.
Feel free to create an account and create your own games.
You can import your sprites and indicate any credit / license.
I recently added a parallax editing feature, you can see it in action here:
https://myshmup.com/games/241
Your feedback is welcome.
Marsatak