1, ArrowChat: facebook alike - https://www.arrowchat.com/
Feature: Chat Rooms, Themes, Notifications, Moderation, Guest Chat, Mobile Chat, Automatic Login,Video Chat, Send Files, Announcements, Block, Applications, Group Permissions
2, Smooch Web Messenger - npm package - https://github.com/smooch/smooch-web
Feature: Sync conversations across every device, easy to integrate, rich messaging
BAD: for IE, ONLY support IE11 above
3, getsitecontrol: well documentation - https://getsitecontrol.com/
Feature: Seamless conversations, Mobile responsive, Targeting, Smart triggers