When I had my WordPress install I used MarsEdit to write and post to my blog. It works via established calls to the database software. As Octopress is a static blog the software runs locally and generates all the pages before pushing them to the proper location on a server.
MarsEdit has basic support for another static blogging engine called Blosxom (which is what this blog used back in 2003). Using the Blosxom support in MarsEdit I was able to write a script to take in the saved file, generate a new post, put the text from the saved file into the new post, optionally commit and push in the Octopress git repo, and then use the Octopress software to generate and deploy the new version of the blog.
It’s quick. It’s a bit dirty. But here it is for anyone to use. You can find the script on github as octomars.