I have been a happy user of Ebitengine for several years. If you are interested in seeing the source of some games created with it, check out the awesome-ebitengine list.

https://github.com/sedyh/awesome-ebitengine

All of the games listed on my itch.io profile were created using Ebitengine, and they are all open source.

https://rocketnine.itch.io