Love the style of the MailChimp's 2016 Annual report. Also 246,148,661,219 emails sent in a year is definitely an impressive number.
Speaking of annual reports, I enjoyed reading SkyVerge's 2016 Year In Review. The majority of SkyVerge's work is with WooCommerce and maintains almost 70 plugins for it. I found their coverage of the plugins they refactored particularly interesting – along with their rewrite of the highly popular Product Customizer app.