Spreading Thankfulness in Open Source.
saythanks.io will provide a button/link for use by open source projects, to encourage users to send a simple thank you note to the creator (or creators) of that project.
This simple button/link can be added to READMEs and project documentation.
The author can then enjoy a nice inbox (ideally) filled with very small, thoughtful messages from the happy users of the software they enjoy to toil over.