I'm having trouble understanding the question—there's plenty of open-source games that do not use ECS or a Unity-style scene graph. this mode of thinking being the default is relatively recent in the history of video game development. if you've never tried something like that before, PICO-8 might be a good starting point. this blog post might also prove useful: https://www.gamedev.net/blogs/entry/2265481-oop-is-dead-long...
I've only slightly dabbled in game engines, and have only been exposed to ECS and scene graphs, so I was asking for other methods, since they don't seem to be nearly as popular. Searching gives me results, but I can't qualify them, so maybe aren't "interesting" to actual game devs. I added "practical" because this is HN, where sometimes theoretical tangents take hold. :)
Honestly I think most sensible ways of organizing renderable entities end up approximating either ECS or scene graphs. The difference is that you’re doing the management yourself instead of relying on engine’s functionality, so you get way less features but way more performance due to lack of unnecessary overhead.
There are kinds of games where simply having a input handling function, logic tick function and draw function executed in a big loop is pretty much all you need, and I assume that's what GP is talking about. I like to write games this way on game jams and it serves me well.
OTOH, there are also kinds of games that I simply wouldn't dare to write this way without figuring a solid abstraction out first, and things like ECS can often fit pretty well for that.