List of some useful open source tray tools I use daily.
Easy window management: SpectacleThe biggest issue I have with OSX is the way window management is handled. Simple tasks such as sizing an editor and browser so both are visible between the left and right side of the screen is cumbersome, especially with a touch pad. The simple task of maximizing a window never seems to work as expected.
Spectacle fixes these issues by providing a bunch of hot keys which you can customize to your needs. It also has a full screen that works.
Some examples are on the homepage
System fan control: smcFanControlThis is a great app to keep your for MacBook nice and cool. With smcFanControl you can monitor temperatures, as well as customize the fan speed.
Graphics monitoring: gfxCardStatusThis is a simple app that lets you monitor which graphics device is currently in use. It also lets you override which card is use such as using the integrated GPU instead of the discrete to save battery life.
Quick image sharing: ImgurBarThe simple image sharer. I am a big fan of Imgur and a quick way to share images with people is by using this app. Simply drag your image to the tray icon (the black dot) and it will handle the upload as well as copying a link to the image to your clipboard.