Complex sentence: On April 2015, following a community dispute, (Owner against CCL) almost all users left Rigveda Wiki, and most of them joined Namuwiki, which is one of the biggest wikis forked from the Rigveda Wiki.
Split into simpler sentences: On April 2015, following a community dispute (Owner against CCL), most of the Rigveda Wiki users left. Most of them rejoined at Namuwiki, which is one of the biggest wikis forked from Rigveda Wiki.