Windows Live Writer is a blog editing and publishing tool that enables the user to write and publish their blog posts to a number of supported blogs simultaneously.
Windows Live Writer has WSIWYG (what you see what you get) type authoring, where users can see what they have created before publishing it. Windows Live Writer comes bundled with Windows Live Essentials, a suite of different Web 2.0 communications tools including Mail, Gallery, Messenger and a few others.
Techopedia explains Windows Live Writer
Windows Live Writer is available as part of Windows Live Essentials and is installed on client machines. Besides blog authoring and publishing, Windows Live Writer provides a few other key features, including formatting, adding photos and videos, and adding a location using Bing Maps. Live Writer integrates easily with YouTube; including just the link in a blog post will immediately provide a preview of the video without any code or API integration.
Windows Live Writer supports all blogs that incorporate real simple distribution (RSD), a blog publishing format in XML, and is compatible with major blog publishing sites, including Blogger, WordPress and TypePad.