Shtuff Chat - Free Group / Team chat with persistent history.
Big Ass Message - The most useful single-serving site on the World Wide Web.
Discord History Tracker - Discord History Tracker is a great tool that enables you to select chat history and save it in your private conversations, servers, groups, and then view it anytime without needing an internet connection.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
PieMessage - iMessage on Android
JabbR - A chat application built with ASP.NET and SignalR.