The full experience of Dynaeleos is free! But if you feel like supporting the developer, paying $1 or more gives you access to the Declassified Edition, which contains the full game with its files unarchived, meaning you get access to the game's raw assets, script, and code. You're free to inspect the code and use them for your own projects.
The Declassified Edition also comes with a folder of bonus material: the soundtrack (also accessible from the unarchived game) plus one unused original song, a CG collection (also accessible from the unarchived game), and four bonus images, including the main character's rough design sketches.