Let's Chat is a persistent messaging application that runs on Node.js and MongoDB. It's designed to be easily deployable and fits well with small, intimate teams.
License: Open Source
Let's Chat is a user-friendly, open-source chat platform suitable for small teams with basic chat needs, while Riot.im (now Element) offers advanced features like end-to-end encryption and video conferencing, making it more suited for organizations focused on privacy and collaboration. The choice largely depends on the users' priorities, whether they value simplicity and ease of use or advanced security and feature richness.