Reading some more around the organisational culture at Buffer, I came across iDoneThis. It's a simple productivity app that (as you can see above) sends staff a reminder email each evening asking what they did that day. The next day, staff get a digest with what everyone on the team managed to get done.
As Leo Widrich (co-founder/COO) of Buffer says, they use it to not only focus staff on what they've accomplished but how they are working to develop. It's part of their commitment to have a focus as part of their organisation culture on self-improvement. As all improvements are shared across the team it's a great way, says Leo, to make progress visible, get encouragement, find a habit, and can act as a prompt to learn new skills. Nicely done.