Hulu, Living Social, All of 37 Signals, Groupon, AirBnb, Scribd, Zendesk, Soundcloud, etc.
Twitter's scale is unlike nearly every single web app online, so I think the real story with Rails and Twitter isn't that "they had to move away from it for scalability reasons," but rather it's amazing that they were table to leverage Rails for as long as they did."
Also, Twitter is more dropping Ruby all together rather than just Rails specifically. Again, this isn't to say that Ruby isn't a great language that works for most people (it let Twitter grow quickly to where they are today), but at their scale with their demands it doesn't work well.
Twitter's scale is unlike nearly every single web app online, so I think the real story with Rails and Twitter isn't that "they had to move away from it for scalability reasons," but rather it's amazing that they were table to leverage Rails for as long as they did."
Also, Twitter is more dropping Ruby all together rather than just Rails specifically. Again, this isn't to say that Ruby isn't a great language that works for most people (it let Twitter grow quickly to where they are today), but at their scale with their demands it doesn't work well.