Microsoft has launched Windows Live Writer. This is a free, downloadable application that runs on your Windows PC and allows you to write blog posts.
Since most blogging tools are web based and not all allow WYSIWYG editing (where you see on screen exactly how the blog post will look), Windows Live Writer will be useful for some writers looking for a faster, easier way to post to blogs.
Tools like this have been around for a long time. For example RocketPost is another company in this space, although they charge $12 for their software. Performancing (a Firefox plugin that people rave about) and Ecto (Om Malik uses this one) are two others. The biggest complaint about these existing services was that editing existing posts is difficult or impossible.
Windows Live Writer has a lot of bells and whistles - preview in WYSIWYG or HTML mode, support for most blogging platforms (Windows Live Spaces, Blogger, LiveJournal, TypePad, WordPress and others), easy insertion of photos and things like Live.com Maps, and tagging. Good stuff, but none of it differentiates it from existing year old products.
What does differentiate Live Writer is that they've released an API that allows developers to extend the capabilities of the software to publish additional content types.
Too bad that, like Google and Picasa, Microsoft has ignored the Mac platform.