An artist got tired of the same UV annoyances, so he wrote his own add-on.
Then he put it on GitHub for free, submitted it to Blender's Extensions platform, and shipped it with a Japanese UI as well as English — which almost nobody bothers to do.
That's Mio3 UV v1.0. Small tool, unusually thoughtful release.
The best tools in this industry are still mostly built by one annoyed person.
What's the best free tool you use that was made by a single developer?