It’s posterity, the exciting new Python mail client (as web server) with some mods (that’s my bzr branch) to support plug-ins slightly more and new chrome ‘decorators’. Into that we have plugged “visterity”, a new visophyte-ish thing. (Found in the visophyte bzr trunk under src/visterity-py) This works with the cairo renderer (so have python-cairo), and may work with the aggdraw renderer, but I haven’t tried it and make no promises.
To elaborate on the graphic, it’s posterity’s conversation view with the visterity plugin providing a png at a chrome decoration point (‘conversation’, ‘top’). It is not yet click-able! It is most definitely not responsive to what the current message you are dealing with is. However, those are the next steps!
I will likely implement a mixed svg/js renderer that should then be able to interact bidirectionally with posterity. This is what I have been hoping to do with Thunderbird but have been punting on because it involves a degree of pain/difficulty that is hard to justify given my limited hobby-programming time. However, Thunderbird is still on the map and I will attempt to ensure the implementation is general enough that I can plug it into Thunderbird as well.