The Stellar network did fork when we running on a fork of legacy software. Since then, we have rebuilt the entire consensus system using a completely different consensus system. The underlying consensus system was designed by Prof. David Mazieres, head of Stanford University's Secure Computing group - you can read the white paper here: https://www.stellar.org/developers/learn/concepts/scp.html A completely new implementation of SCP in the form of stellar-core was completed earlier this year. You can read about it here: http://graydon.livejournal.com/227874.html