LeapChat

Teamchat solution similar to Gitter.im or Slack.

Self-hosted / cloud notification infrastructure for developers.

Platform for secure collaboration across the entire software development lifecycle, can be integrated with Gitlab (alternative to Slack).

Customer communication platform (alternative to Intercom & Zendesk).

Zulip is a powerful, open source group chat application.

Push notifications to phone or desktop using HTTP PUT/POST, with Android app, CLI and web app, similar to Pushover and Gotify.

Apprise allows you to send a notification to almost all of the most popular notification services available to us today such as: Telegram, Discord, Slack, Amazon SNS, Gotify, etc.

Instant messaging platform. Backend in Go. Clients: Swift iOS, Java Android, JS webapp, scriptable command line; chatbots.

Notification server with Android and CLI clients (alternative to PushBullet).

Fully-featured Matrix client for Web, iOS & Android.

Language-agnostic real-time messaging (Websocket or SockJS) server.

Conversational app builder (alternative to Typeform or Landbot).