Browser-based writing, calculator and spreadsheet. Seamless compatibility with MS Office. Created a bridge, can send documents back and forth. Anywhere, any time access, 1 gb of online storage, collaboration support. Simple document management. Free. May put ads in future versions, using contextual ads but without invading privacy.
Mashup API, take Office documents, and want to show them to readers of your blog, e.g. you want to show an Excel spreadsheet to people on your blog, currently you have to either download Excel spreadsheet or convert to an image. So can instead use ThinkFree API.
There are also browser extensions for Firefox or IE to view any link to office document inside the browers. OS X dashboard, Google and Yahoo widgets. Also a WordPress plug-in.
Can convert, say, Powerpont into Flash. Spreadsheets are turned into HTML, and it looks almost identical to the original. Viewer.thinkfree.com