Without exaggeration in my mind, Zimbra is a company that is at least 2 years ahead of the game in terms of rich, browser-based application development. Two years is light years when it comes to software development. From a developer's perspective, this is the most compelling application I have seen on the internet, given it's rich, deep, browser based interfaces, and unparalleled functionality. They simply "got it right" and have set a high-water mark for others to set their sights on, while seemingly just beginning to push forward. With tremendous respect to Google, I would put this application above Google Maps in terms of technical accomplishment on the client-side UI design and execution. I say this especially given the fact that they did it when very few, if any, AJAX frameworks were in existence, let alone organized. Even today many of us are eagerly awaiting Open AJAX (which, not coincidentally, Zimbra is active as a collaborator).
Zimbra has targeted a ubiquitous application realm -- email, messaging, rss, net phone, calendar, contact managing, all integrated into one "business collaboration" app. (demo) It's a tall order to capture market share in the area of email clients, with so many players in the market, but if you take a look at the design and execution of this browser-based application in the demos of the product, it's very tight, feature rich, while also being completely intuitive and familiar looking to its PC-based ancestor. It's more than all of that though. It's absolutely inspiring in the manner in which they have innovated with AJAX interfaces and web-services to deliver a seamless integration between mail, news feeds, emerging mapping applications, and even internet telephony. It doesn't feel at all like a traditional web application, yet it is seamlessly integrated into the web. Examples that I particularly like include: within the body of an email hovering your mouse over phone number text gives you the option to directly call this person using your preferred VOIP service, like Skype or Google Talk, with the click of the link; hovering over a name automatically generates that contact's information; mouse over a date and it will pull up your appointments for that day; hover over a web-link and it shows a thumbnailed screenshot of that webpage as a preview; tag based searching, and even searching within attachments, search for Amazon books within the email client... What I find paradigm-shattering is the manner in which it is all accomplished -- it is all built using web standards, AJAX, plus server and web-service (SOAP) calls.
Zimbra and their touchstone app, "Collaboration Server", more than any one existing application I've seen, is the first to demonstrate clearly that the 'game' has changed, from a pc-based paradigm to a web-based one. I say this with knowledge and respect for the level of progression and proficiency from cornerstone browser-based applications Gmail, Google Maps, Google Suggest, Yahoo Maps. This feels just a cut above because of the rich and complete functionality and apparent maturity of their implementation and the fact that they have pioneered the use of the technologies here, many of which are captured in their free, open-source Ajax Toolkit that they openly share with the community: AJAXTK.
The company is also directed by some of the web-digital elite, as can be seen by those on their Board, with seminal figures from Netscape, BEA and guiding presences from those involved with NetFlix, RedHat and open-source stalwarts like mySQL. This is also clearly evidenced in small part by the open, coooperative communication they offer regarding their strategy and philosophy. They are openly engaging the community for ideas, concepts, along with technology partners for 'Zimlits', while giving us individual developers an AJAX Toolkit (AJAXTK) so that we can utilize some of the same libraries and high level function calls they have used in construction this remarkable application.
If you are a developer, or just someone interested in technology, you have to check out the hosted demo to see for yourself what is the present and near-future cutting edge of interface design and execution on the web. This is a great inspiration on many levels to me.