These builds are rarely distributed by reputable organizations. They are typically hosted on file-sharing sites, private forums, or torrent trackers.
Anecdotal benchmarks suggest these "Extreme" builds can reduce the installation footprint from approximately 15-20 GB to under 4 GB. RAM usage on idle has been observed to drop from ~1 GB to ~400 MB, making the OS viable for systems with only 2 GB of RAM. Windows 8.1 Pro Super Lite Extreme 32 64-bit