Onix Client is a client-side mod for Minecraft Bedrock Edition. (here's their website)
But it also includes a scripting API, allowing you to create your own mods in Lua by paying ~5$ a month for the premium version. This really got me interested as soon as I heard about it, and at this point I'm one of the scripters who's been around the longest.
I've put a lot of time into some of these projects, and most of my best ones were never released because when releasing something for the public to use, it's kinda gotta be good. And it turns out that I'd rather move on to 3 more complicated projects before polishing the first, so I end up with a ton of super complex but only mostly working mods.