Please, read carefully before asking questions. Official Release, Steam's outdated. Enjoy it and have fun

What does it do:

Completely removes slope requirements for buildings so they can be placed in any terrain.
The terrain gets removed from inside of the buildings, so it can be placed as much as inside mountain walls.
Increase vertical position tolerance, so players can make their buildings as high as there's foundation underneath (Default ' - and = ')
All that can be done without the development tool, so you don't need to cheat and move the structure. Just place buildings like usual
Should work with your previous save (no need to New Game or Import) and just about any mod, even those that deal with buildings and new towns. Just make sure to set Slopeless at the bottom of the mod order list

Known issues:

Buildings still follow slopes. You just 've got to hold your change slope hotkey (Default ' ] and [') and it snaps perfectly
Buildings with balcony inside the terrain mess up. People can go upstairs and teleport above ground and that screws up pathfinding too. Just don't use buildings with balcony inside hills if you don't want that to happen
Hills cutting through balcony have no collision but they do appear. Doesn't screw people navigation and actually looks pretty cool, but ideally people would be able to climb that leftover piece of terrain instead of ignoring it
Doesn't help much with walls. It does allow you to place them anywhere but it still looks weird
Removes building collision with other buildings. Overlapped buildings behaviour is such that both buildings keep it's collisions and textures, but the overlapped section haven't pathfinding. This means that they work actually fine and that's just a aesthetic concern that players can avoid. Also a little bit of overlapping, specially as long it's unreachable parts colliding (foundations) actually makes sense and is completelly harmless
When trying to zoom and look from inside buildings inside cliffs the camera colides with the hill. Easily manageable but a little annoying

This mod isn't deeply tested. Any oversight, suggestion and feedback is welcome.