Gmail has enjoyed phenomenal success, and regardless of which study you choose to look at for exact numbers, there's no doubt that Gmail is towards the top of the pack when it comes to market share. For certain circles, Gmail has become synonymous with email, or at least with webmail. Many appreciate its clean interface and the simple ability to access their inbox from anywhere.

But Gmail is far from the only name in the game when it comes to web-based email clients. In fact, there are a number of open source alternatives available for those who want more freedom, and occasionally, a completely different approach to managing their email without relying on a desktop client. You'll still need an email server to use with these clients. If you don't already have a favorite, look for an upcoming article with some options to consider.

Let's take a look at just a few of the free, open source webmail clients out there available for you to choose from.

Roundcube

First up on the list is Roundcube. Roundcube is a modern webmail client that will install easily on a standard LAMP (Linux, Apache, MySQL, and PHP) stack. It features a drag-and-drop interface that generally feels modern and fast, and comes with a slew of features: canned responses, spell checking, translation into over 70 languages, a templating system, tight address book integration, and many more. It also features a pluggable API for creating extensions.

It comes with a comprehensive search tool, and a number of features on the roadmap, from calendaring to a mobile UI to conversation view, sound promising, but at the moment these missing features do hold it back a bit compared to some other options.

Roundcube is available as open source under the GPLv3.

Roundcube screenshot courtesy of the project's website.

Zimbra

The next client on the list is Zimbra, which I have used extensively for work. Zimbra includes both a webmail client and an email server, so if you're looking for an all-in-one solution, it may be a good choice.

Zimbra is a well-maintained project that has been hosted at a number of different corporate entities through the years, and was acquired by Synacore in 2016. It features most of the things you've come to expect in a modern webmail client, from webmail to folders to contact lists to a number of pluggable extensions, and generally works very well. I have to admit that I'm most familiar with an older version of Zimbra, which felt at times slow and clunky, especially on mobile, but it appears that more recent versions have overcome these issues and provide a snappy, clean interface regardless of the device you are using. A desktop client is also available for those who prefer a more native experience. For more on Zimbra, see this article from Zimbra's Olivier Thierry, who shares a good deal more about Zimbra's role in the open source community.

Zimbra's web client is licensed under a Common Public Attribution License, and the server code is available under GPLv2. S

Zimbra screenshot courtesy of Clemente under the GNU Free Documentation License.

SquirrelMail

I have to admit, SquirrelMail (self-described as "webmail for nuts") does not have all of the bells and whistles of some more modern email clients, but it's simple to install and use and therefore was my go-to webmail tool for many years when I was setting up websites and needed a mail client that was easy and "just works." As I am no longer doing client work and shifted towards using forwarders instead of dedicated email accounts for personal projects, I realized it had been awhile since I took a look at SquirrelMail. For better or for worse, it's exactly where I left it.

SquirrelMail started in 1999 as an early entry into the field of webmail clients, with a focus on low resource consumption on both the server and client side. It requires little in the way of special extensions of technologies to be used, which back when it was created was quite important, as browsers had not yet standardized in the way we expect them to be today. The flip side of its somewhat dated interface is that it has been tested and used in production environments for many years, and it's a good choice for someone who wants a webmail client with few frills but also few headaches to administer.

SquirrelMail is written in PHP and is licensed under the GPL.

SquirrelMail screenshot courtesy of the project website.

Rainloop

Next up is Rainloop. Rainloop is a very modern entry into the webmail arena, and its interface is definitely closer to what you might expect if you're used to Gmail or another commercial email client. It comes with most features you've come to expect, including email address autocompletion, drag-and-drop and keyboard interfaces, filtering support, and many others, and it can easily be extended with additional plugins. It integrates with other online accounts like Facebook, Twitter, Google, and Dropbox for a more connected experience, and it also renders HTML emails very well compared to some other clients I've used, which can struggle with complex markup.

It's easy to install, and you can try Rainloop in an online demo to decide if it's a good fit for you.

Rainloop is primarily written in PHP, and the community edition is licensed under the AGPL. You can also check out the source code on GitHub.

Rainloop screenshot by author.

More options

• Mailspring is a new option that supports multiple accounts, read receipts, translations, undo send, and other popular email client features. It is a fork developed by one of the creators of Nylas Mail, which was maintained until Spring 2017.
• Cypht is a lightweight email client and news reader written in PHP and JavaScript and licensed under GPL v2. It was developed by the creators of HastyMail, an older GPL-licensed email client.
• Mailpile is an HTML 5 email client, written in Python, and available under the AGPL. Currently in development, Mailpile focuses on speed and privacy.
• WebMail Lite is a modern but minimalist option, licensed under the AGPL and written mostly in PHP.
• Open WebMail is a GPL-licensed client that aims to provide efficient memory management for very large mail files. 
• Kite was on the list the last time we published this review, but it's now obsolete. It was designed to go head-to-head with Gmail, and it's too bad the project didn't advance.
• There are also a number of groupware solutions, such as Horde, which provide webmail in addition to other collaboration tools.

This is by no means a comprehensive list. What's your favorite open source webmail client?