What are some alternatives?
When comparing Roundcube and Rainloop, you can also consider the following products
Mailpile - Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features.
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
SOGo - SOGo is groupware server with a focus on scalability and open standards.
Squirrelmail - SquirrelMail is a standards-based webmail package written in PHP.
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.