NBTExplorer
A graphical NBT editor for all Minecraft NBT data sources
NBTExplorer is an open source graphical NBT (Named Binary Tag) data editor for Minecraft. It supports reading and writing in a number of formats including Standard NBT files (e.g. level.dat), Schematic files, Uncompressed NBT files (e.g. idcounts.dat), Minecraft region files and more.