waffle.io was github projects, built on top of the github api, a few years before github projects. basically a github-based kanban board. It was pretty great if you were a smallish startup.
Plus, an add-on service like that was just begging for GitHub to add the feature themselves, so the company always had an end-of-life looming.
One possible exit was GitHub buying them, but I'm sure GitHub would rather build the feature natively (as they did, right?) for technical reasons. Another is expanding to a standalone service, but GitHub and Trello already owned each side of that space.
It always looked like a technically interesting product but one that I wouldn't use myself and which had no future.