This is the tenth and final post in ReadWriteWeb's series of top products of 2008. Here are the previous nine:

• Top 10 Semantic Web Products of 2008
• Top 10 International Products of 2008
• Top 10 Consumer Web Apps of 2008
• Top 10 RSS and Syndication Products of 2008
• Top 10 Mobile Web Products of 2008
• Top 10 Enterprise Web Products of 2008
• Top 10 Real World Web Apps of 2008
• Top 10 Digital Lifestyle Products of 2008
• Top 10 Alternative Search Engines of 2008

Note: unlike some of our previous lists, we've attempted to order this one according to impact in 2008.

1. iPhone SDK

ReadWriteWeb named Apple as our Best BigCo of 2008, largely due to the iPhone platform. The iPhone truely reached a mainstream audience in 2008, when the 3G iPhone was launched to much acclaim in July. But more significant than the phone itself was the simultaneous launch of the Apple App Store. There were 552 applications available at launch and at time of writing that's risen to over 10,000 applications. So in less than 6 months, the number and variety of iPhone apps has expanded greatly. Indeed, any startup worth its salt has an iPhone version of its web app - the ultimate proof of a successful Web platform.

For many years now everybody (including us) has been predicting that the next year will be the one that the Mobile Web breaks through. 2008 was finally that year - and it's mostly thanks to the iPhone development platform.

2. OpenSocial

November was the first anniversary of Google's OpenSocial, an open API framework for social networks and websites. During 2008 OpenSocial gained a lot of traction; statistics released in November stated that OpenSocial had reached 675 M registered users at that time and there were 7,500 applications.

Most impressive is the list of organizations who signed onto OpenSocial and are actively developing apps for it. That high powered list includes MySpace, AOL, Bebo, hi5, LinkedIn, Ning, Orkut, Yahoo!. Of course still missing from OpenSocial are Facebook and Microsoft, but at the rate OpenSocial is ramping up - they may not need them.

3. Adobe AIR

As we noted in our Best BigCo 2008 post, this was a year in which Adobe's 'Rich Internet App' strategy bore some juicy fruit, with many compelling apps released that were built using AIR (Adobe Integrated Runtime). AIR is a platform that makes it easy to build attractive Internet connected applications that live outside the browser. Last year we noted its potential - AIR was called 'Apollo' for much of its beta - but in February 2008 AIR was officially launched and soon we saw a lot of stunning apps emerge. For examples, check out:

• 6 Adobe AIR Apps to Check Out
• 10 Adobe AIR Apps Bloggers Will Love
• Adobe AIR Goes to Work: 6 Apps for the Corporate Desktop

We've named it our number 3 Web platform of the year, because it breathed new life into Rich Internet Apps this year.

4. Twitter API

The importance of Twitter's API to its success this year can't be overstated. The number and variety of Twitter reader clients alone is amazing, let alone the many other ways Twitter's data is being used (e.g. for e-commerce purposes). It must be said that Twitter has experienced much downtime and many technical glitches throughout the year, but even so it has continued to expand its API service. As Twitter co-founder Biz Stone said a ReadWriteTalk interview last September:

"The API has been arguably the most important, or maybe even inarguably, the most important thing we've done with Twitter. It has allowed us, first of all, to keep the service very simple and create a simple API so that developers can build on top of our infrastructure and come up with ideas that are way better than our ideas ...

So the API, which has easily 10 times more traffic than the website, has been really very important to us. We've seen some amazing work built on top of it from tiny little mobile applications like an SMS timer that just allows you to set a reminder over SMS to call your mom or something like that, to more elaborate visual recreations of Twitter like twittervision.com, which shows an animated map of the world and what everyone's doing around the world with Twitter. ... The [Twitter] API has really been a big success for us, and it's something that we want to continue to focus our efforts on, looking forward."

5. Facebook Platform

Facebook continued to become more popular throughout 2008, reaching 140 million active users by end of the year and growing at a rate of 600,000 users each day. For that reason we gave it an honorable mention in our Best BigCo 2008 post.

However in terms of the Facebook platform, overall we felt that Google's OpenSocial overshadowed it in 2008. As we wrote in our mid-year review, Facebook Platform: The Fanfare Revisited, when the Facebook platform debuted last year it was touted as the next big thing. You no longer needed to bring the audience to your app. Instead your app could be delivered to one of the largest audiences around the web. And not just delivered, but injected into a massive social network. But while it started great, it turns out things are not that simple. Three fundamental issues surfaced:

1. Technical: Should the app be just a teaser that leads users to their site or should it be a duplicate and have full functionality?
2. Business: If e.g. New York Times builds a Facebook app, will it be economic for them (since there's little revenue in Facebook)?
3. Provider costs: Does it pay for Facebook to maintain the platform? As a business with a huge valuation, Facebook needs to maximise profit.

Despite these issues, Facebook's platform shows no signs of slowing and many startups have ported their web apps to Facebook. It may not be the bee's knees anymore, but it's still a very effective platform for startups to utilize.