Windows/Mac/Linux: Are you a fan of Notational Velocity, our favourite note-taking app for Mac, but wish it was available for other operating systems? nvPY is an open-source clone of the app that offers most of the same features for the low price of free.
nvPY syncs flawlessly with Simplenote and lets you store your notes in Dropbox or another cloud storage service. It even does partial auto-syncs in the background so you can work without having to stop and save every five minutes. You can search note names and contents from the search bar, and the app supports Markdown. In fact, the only thing the app doesn't allow you to do is save your notes as a directory of plain text files.
The app requires a little work to install, but once you have it up and running, it works flawlessly. If you use Notational Velocity on the Mac and want something similar for Linux and Windows, give nvPY a try.