
Description: Isotope Mail Client is an open-source, privacy-focused email client for Windows, macOS and Linux. It supports end-to-end encryption using PGP and aims to provide a simple, easy-to-use interface while still allowing advanced configuration options.
Type: Open Source Test Automation Framework
Founded: 2011
Primary Use: Mobile app testing automation
Supported Platforms: iOS, Android, Windows

Description: Rainloop is an open-source webmail client that can be self-hosted. It has modern features like conversation threading, contact management, calendar, and more. It's lightweight, customizable, and works great for personal or business email.
Type: Cloud-based Test Automation Platform
Founded: 2015
Primary Use: Web, mobile, and API testing
Supported Platforms: Web, iOS, Android, API