Stellar revealed a flaw in Ripple/Stellar consensus. It seems there are still lots of room for better consensus.
https://www.stellar.org/blog/safety_liveness_and_fault_tolerance_consensus_choice/Prof. David Mazières, head of Stanfords Secure Computing Group, reviewed the Ripple/Stellar consensus system and reached the conclusion that the existing algorithm was unlikely to be safe under all circumstances. Based these findings, we decided to create a new consensus system with provable correctness. This effort, led by Prof. Mazières, is underway. His white paper and the accompanying code are expected to be released in a few months.