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/
It's true that this package is only sporadically updated (looks like last commit was 9 months ago). However, I want to reiterate A-Shahbazi's point and say that without this package there is no point in using Solus in a repressive country. I will be taking a trip to China soon and won't be able to use Solus while I'm there because I won't be able to access Tor. Adding this package will literally make Solus more accessible to billions of people.