A lot of b2b services have adopted that design style. https://www.octobat.com/ - https://baremetrics.com/ - https://www.intercom.com/

More I can't think of right now...

Stripe's current design went live sometime in September 2016. Mixpanel's went live somewhere in Jan 2017. For a design overhaul of this scale, it's unlikely there was any 'inspiration'.

Yeah, that is very similar. Especially the dropdowns.