Ranked in these QuestionsQuestion Ranking
Supports REST, WebSockets and MQ protocols.
Pro Realtime through filters
You do not connect to classic rooms but to search filters and can be warned of changes on permanent storage or volatile one.
Pro Open Source
Kuzzle is open source and it's released under the Apache 2 License.
Con May have issues since it's stil la relatively young project
Kuzzle is (as of February 2nd, 2015) in alpha version and approaching beta.