The only mobile OS to allow alternate keyboards is Android, but that doesn't stop developers from releasing standalone keyboard apps for iOS and WP7. Sliding Keyboard is the first gesture keyboard to make it to the WP7 Marketplace and has been updated to version 1.7. The idea is the same as other gesture keyboards, the most well known of which is Swype, but unfortunately, the execution leaves a lot to be desired.
Like any other gesture keyboard, Sliding Keyboard allows you to swipe from one letter to the next rather than typing. For shorter words, it may not always be faster, but for longer words, gesture keyboards make phones much more useful. Sliding Keyboard is a standalone app, because WP7 doesn't support alternate keyboards. That means you'll have to rely on copy/paste to get your text from the Sliding Keyboard app for most things, although the app does integrate SMS, e-mail, and Bing search, which helps immensely. The app also supports 9 languages: English (US & UK), Catalan, French, German, Italian, Spanish, Hungarian, and Polish.
All of that sounds great, but as you'll see in the video, there is a reason why the app has garnered mostly bad reviews. There is a notable delay after finishing a gesture before the word suggestions pop up, and the auto-suggest clearly needs more work.
Sliding Keyboard is available in the Marketplace for 99 cents.
Before Anna there's also the Baidu QWERTY keyboard. Only reason N8 dosn't have as many v.keyboard variaties as Android is because of the Developer support.
Big Thanks to eLOPE for killing them off. A job well done.