Rainbow is described as 'Unified Communication as a Service (UCaaS) and Communication Platform as a Service (CPaaS). It is a hybrid cloud solution for enterprise communications which aims to connect people and systems optimally' and is an app in the Office & Productivity category. There are more than 10 alternatives to Rainbow for a variety of platforms, including Mac, Windows, Android, iPhone and Linux. The best alternative is Slack, which is free. Other great apps like Rainbow are Microsoft Teams (Freemium), Ripcord (Free Personal), Threads (Freemium) and Plumm (Paid).
LeggoChat is a group or channel based chat platform that is designed to be easy to set up for any casual, or formal settings and discussions. Users can choose to have their messages logged and stored, or otherwise. No user accounts are required to get started at all.
PrivMX is safe and easy collaboration software for all kinds of teams, with virtual workspace protected by end-to-end encryption. Each team uses desktop/laptop client software and its own (zero-knowledge) PrivMX Team Server.