It provides a Level class that has the same fields as the java one:
public string name;
public string creator;
public long createTime;
public int width;
public int depth;
public int height;
public byte blocks;
public int xSpawn;
public int ySpawn;
public int zSpawn;
public float rotSpawn;
To use it in C# add "using com.mojang.minecraft.level;" to the top of your code. Don't change the namespace, it's needed to be compatible with the server's Java serialization.
To load a map use "Level.Load( fileName );" and to save use "lvl.Save( fileName );"
It also includes:
A constructor with size parameters: "Level lvl = new Level( width, depth, height );"
Methods to get/set createTime using .NET DateTime: "GetCreateTime();" and "SetCreateTime( dateTime );"
Methods to get/set a tile and an enum with currently supported tiles: "GetTile( x, y, z );" and "SetTile( x, y, z, t )"
A "Clear()" method that sets all tiles to air.
It does not include other useful methods such as "findSpawn()" of the server's Level class as that would require a decompile or writing them from scratch (which I won't do).
To use it either add a reference to MinecraftLevel.dll on your .NET project (you must also have the 3 IKVM dlls on the same folder but there's no need to reference them) or use the source code provided to integrate directly with your code.