Chisels & Bits
A block customization mod that includes a radial menu of chisel modes, multi material blocks, and reusable bits that are dropped by the chisel and can be added back on to the modified block. Blocks can be customized down to the individual pixel (1/16th in each dimension, or more rapidly by choosing the appropriate tool mode.
Chisels & Bits is written and maintained by AlgorithmX2 for the latest Minecraft releases. Source code is available on Github for anyone who wants to backport to Minecraft 1.7 or earlier.