S2TC's format specification is very easy to implement, so it is not hard to make
a working compressor or decompressor for it. It is based on Color Cell
Compression from 1986, and decoding is done entirely using the methods from
there. Encoding is done using a search and refinement method that is derived
from the methods described in that paper.
This also makes this format a great platform for learning about texture
compression and how to tune a compressor for best quality.
S2TC is especially well suited for runtime (on-load) compression of textures, as
it is - in low quality settings - way faster than any other texture compressors