there is also
@Tuhalu positional guide
Reference: Positioning Placeable Items
An online app that checks your .json files for consistency.
http://jsonlint.com/
@MelOzone palette guide and a website for getting color information.
More lights from Mel (and other modelling stuff)
http://paletton.com/
A website to check out other folks mods
http://praisedb.x10.bz/
Free downloadable voxel editors
Such as MagicaVoxel https://voxel.codeplex.com/
and Voxel Shop
VoxelShop (Voxel-Editor) | Terasology
I hope this helps