Sorry I'm late, didn't have hnreplies set up.

Sure! For the past 10 years I've been making a 2D skeletal animation tool. It's a desktop app built with Java, so I get all the nice Java tooling, hotswap, etc. There's no Swing junk and it's not built like most productivity apps. It's built like a game using OpenGL and runs at 60+ FPS. It uses a lot of my own OSS, like libgdx and my 2D UI framework scene2d.ui. NIH is a thing but there is also a lot to be said about not needing to rely on others and wade through their messes. With this setup my productivity is super high.

Instead of scaling up the company and moving from a dev role to one of those nasty spreadsheet people, I stayed doing what I like. Even after 10 years I'm still the only developer on the desktop app, so all the code is mine from the start. No cruft! It's either pristine or my own uglies. I ran the company lean as long as possible. That was something like 5-6 years working long days, but I like working on it. Nowadays it's more relaxed and a handful of others work on runtimes and customer support.

I wrote this blog post 10 years ago, just after the app first saw some success:
http://esotericsoftware.com/blog/building-spine

The trick for me was to fill a niche that I was familiar with and leverage the tools and libraries I had already been working on for a long time. There were competitors already established in the niche. The now defunct Spriter had a 9 month head start. Flash actually comes close to competing, but you need to extract the animation data from it and write your own runtimes.

That is probably another reason Spine is successful. There are many tools for doing animation: Blender, After Effects, Moho, Toon Boom, etc. Those can be impressive if you're exporting video (eg making cartoons) but they aren't easy to bring into a game. Spine is similar in that you can make animation, but it also provides runtimes to render the animations in games/apps. Only a few competitors do that, and they do it pretty poorly as an add-on, while it's a main feature for Spine.

Spine is also set apart with a focus on good (if nonstandard) UI/UX, workflow, and polish. There are no right click context menus anywhere. That was a sort of experiment, but I like it. It forces placing functionality in UI that is discoverable. One reason UI is so important is that Spine succeeds by making the workers happy. Make a tool people love to use and they'll naturally push the businesses they work for to buy it, if only so they don't have to suffer some other tools. Couple that with Robin Hood style pricing so you are affordable for individuals but more expensive for businesses who can both afford a higher price and stand to gain more from using the tool.

I greatly dislike subscriptions. I won't buy any software that is subscription only, absolutely not ever. Given that, I also won't sell my software that way. Instead I sell to individuals a perpetual, lifetime license that gives ALL future updates. Some think that is crazy, leaving money on the table. It costs to bugfix and develop new features right? IMO it doesn't matter. It's more important to have many individuals using the latest version who will be proponents at their jobs. That leads to the next part, which is businesses pay annually. It's the same software, but the cost is per year per seat for a business. That gives recurring revenue and makes up for not gouging individuals with a bullshit subscription.

TL;DR is something boring like: find a niche, find ways to do things better, add value in new ways, and structure pricing to encourage individuals while taxing businesses.