As explained at OpenGL.org, "BPTC Texture Compression is the collective name for a pair of compression formats. One of them is for unsigned normalized images, while the other is for floating-point values. They both use 4x4 blocks, and each block in both is 128-bits in size. Unlike S3 Texture Compression, the blocks are taken as byte streams, and thus they are endian-independent." Additional information can be found via the specification for the GL_ARB_texture_compression_bptc extension.
Intel "Gen7" Ivy Bridge hardware and newer has support for dealing with BPTC. Neil Roberts of Intel's Open-Source Technology Center published the set of six patches for providing the BPTC texture compression support in Mesa. The patches have yet to be merged to Mesa trunk but for now can be found on Mesa-dev and will hopefully land in time for the next (Mesa 10.3) release. Besides this texture compression scheme working with the latest Intel graphics hardware, GL_ARB_texture_compression_bptc is unconditionally supported by Mesa's "swrast" driver.