Why? Necessary to make Tor work in areas where access to the Tor network is blocked.
Open Source: yes
Description: Obfs4 is an obfuscation protocol designed to circumvent DPI-based censorship. It incorporates ideas and concepts from Philipp Winter's ScrambleSuit protocol. The obfs naming was chosen primarily because it was shorter. In terms of protocol ancestery obfs4 is much closer to ScrambleSuit than obfs2/obfs3. Information on ScrambleSuit can be found here: https://www.cs.kau.se/philwint/scramblesuit/