I've forked it from the original MC2MT project by ShadowNinja. Compared to the original project whose mappings map to a Minetest Game mod soup, converting to a MineClone based game such as Mineclonia allows all blocks in the world to be converted as close to 1:1 to their Minecraft counterpart as the current state of Mineclonia allows. My fork also flips the world on the Z axis, something mcimport does to preserve the direction of north in the world (i.e. if you generate a preview of the world with minetestmapper, north will be in the same direction as in Minecraft). There are also some general improvements done to it such as fixing Windows builds, having it write an accompanying world.mt file as well as a worldmod to set the mapgen to singlenode.
Compared to the mcimport tool written in Python, MC2MT is extremely fast, both due to being written in C++ and due to the conversion process being multithreaded. I've converted large Minecraft worlds using this tool (>1GB) that finishes in about a minute or two, that would take several hours with the Python script. The mappings used are partially based off of MysticTempest's MineClone2 mappings for mcimport so MC2MT should convert similarly to those.
The tool works best at converting basic building blocks. More complex blocks with inventories currently don't fully convert over (there is code to convert e.g. chests into their MTG counterpart, but this hasn't been adjusted for MineClone) and will be mostly decorative. Any redstone more complex than a pressure plate is most likely not going to work. Nontheless, if you want to convert an old personal Minecraft world or some Minecraft map download from somewhere, it works fine for exploring it inside of Minetest. Below is how my old Minecraft survival world looks when converted:

For instructions on how to use, see the README. Binary builds are provided for Windows and Linux, otherwise you can compile from source.