With 0.13 the curved rail has been removed. Instead of laying rail tracks by hand using straight and curved rail pieces you can use the rail planner to place the rail for you by clicking the green arrow on an existing piece of rail and then clicking again where the rail should end.
If you prefer the old way of laying curved rail then this mod is for you. It will keep the rail planner in the game but it also adds the curved rail item back into the crafting menu so it can be placed manually.
It will be unlocked at the same time as the rail planner and costs 4x rail to craft. After placing it down it will act as if it was laid down by the rail planner, when picked up again it will result in 4x rail instead of curved rail.
Should you remove the mod from a running game then the curved rail already placed down will stay.
If you have problems or ideas for the mod then make a thread here on the mod portal or send me a PM on the forums.