Google's open mobile OS platform, Android, burst onto the scene this year as a rival to Apple's closed iPhone platform. Google spent a lot of time this year encouraging developers to create applications for Android - and rewarding them for doing so with cold, hard cash with the Android Developer Challenge (see our previous coverage here). This led to many third party apps and multiple App Stores. The first Android phone - the "T-Mobile G1 With Google" - was launched in September, followed by a second Blackberry-like phone in December. Android apps are showing steady growth and we can expect to see this ramp up in 2009 as more handsets come on the market.
Android went open source in October, which starkly set Google apart from Apple's controlled platform. While iPhone was our top platform in 2008, Google has the opportunity to challenge for this mantle next year.
Amazon's leading edge Web Services stack was first introduced to the world in 2006 and it continued to impress in 2008 - albeit with more of a business focus. Amazon Web Services basically became a more mature offering in '08 and it shored up its support services.
Amazon Web Services, led by Simple Storage Service (S3) and Elastic Compute Cloud (EC2), was the first major cloud computing platform and today it powers the backend for many startups. At the beginning of the year we noted that Amazon's web services now accounts for more bandwidth than all of Amazon's global web sites combined. Then in April, Amazon announced premium for-pay support packages for some of its core infrastructure services. S3, EC2 and Simple Queue Service (SQS) each received the gold and silver level support treatment. In October Amazon announced that EC2 was coming out of beta and that it now supported Windows Server 2003 and Microsoft SQL Server (i.e. expanding beyond Linux distributions and OpenSolaris). At the same time Amazon offered a Service Level Agreement for EC2 and promised an availability of 99.95%.
The Live Mesh service launched in April as an invite only "technology preview". It is Microsoft's attempt to tie all of our data together. Live Mesh synchronizes data across multiple devices (currently just Windows computers, but theoretically it will extend to mobile and other devices in the future) as well as to a web desktop that exists in the cloud. It can sync data across devices used by a single users, as well as create shared spaces for multiple users.
Essentially, Live Mesh is a collection of feeds (which can be expressed as ATOM, JSON, FeedSync, RSS, WB-XML, or POX). Every piece of data entered into a user's Mesh -- be it a file, a folder, a message, a user permission, or a new device -- is rendered as a piece of information in a feed. The feeds are then synced with other devices that are part of that Mesh following rules for how to sync each particular piece of information (i.e., File A may sync with Users 1, 2, and 3, while File B may only be told to sync with Users 1 and 2).
Earlier this year Yahoo announced that the closed beta period for its location platform Fire Eagle had ended and that the service was now open for everybody. A number of high-profile services, including Brightkite, Movable Type, Dopplr, and Pownce have implemented Fire Eagle through the numerous APIs Yahoo provides for accessing the service.
As we wrote about Fire Eagle when the beta was first announced, it offers API kits in five different programming languages, it's got user authorization protocols already available for web, desktop and mobile apps and it's using the open standards community built oAuth to facilitate faster, more secure mashups. So this platform is leveraging universal open standards.
Note: also see our coverage of the Yahoo! Internet Location Platform, a collection of in-depth geo-location based APIs.

This year Mozilla announced Weave, a new web platform that will store users' browser metadata in a cloud environment for access anywhere. Weave is a "framework for services integration" that will, according to Mozilla, "focus on finding ways to enhance the Firefox user experience, increase user control over personal information, and provide new opportunities for developers to build innovative online experiences."
The basic idea is that browser metadata (things stored in your Firefox profile like bookmarks, history, RSS feeds, usernames and passwords, etc.) is pushed into the cloud and stored on Mozilla's servers. The data is available to users from wherever they get online and users can share information with friends, family, or third parties while retaining control over how, when, and if the info is shared.

There were many other Web platforms that impressed us during the year. Google's Chrome browser is highly promising (but we felt it was too early to be in the top 10), Google Gears helped take the online world offline, meebo created an intriguing platform based on its core IM capabilities, Bungee Labs developed a great mashups platform, Salesforce.com had a strong year again, and on and on. It seems like every major Internet company nowadays has a platform, which is great for developers and users alike. Check out our earlier post listing 10 promising web platforms for other examples.
We hope you agree with our top 10 list, but we're sure there are one or two platforms you think should be here instead. So let us know in the comments.
Also for more about the theory and practice of platforms, check out these RWW posts: