There have been some posts on the Factorio forums about reimplementing the curved rail into the game because in some situations it's easier to lay curved rails manually than using the rail planner. As the devs are not likely to bring the curved rail back I decided to write this small mod, also partly because it had been a few months since my last mod and I wanted to get back to modding.
For me it was useful practice and as the download count shows at least a small playerbase has been looking for a mod that does this. (Or they are not aware of the new 0.13 rail planner functionality, that's why I added an explanation to the info page just now.)
