Google+.
Google · Vic Gundotra · Technology
Google's social network, mandated across the company's products and abandoned eight years later.

—
Figures undisclosed
7 yrs 10 mo
2011–2019
Poor Product-Market Fit
Built for a demand that never showed up
Everywhere. Used by no one.
TLDR
Google+ launched in 2011 as the company's answer to Facebook, with Circles as its organising idea and integration into nearly every Google product as its distribution strategy. Sign-ups were forced through YouTube comments, Gmail, and search.
Distribution was never the problem. Engagement was: reported session times were minimal, and the network never developed the everyday social gravity it needed. A pair of API bugs that exposed user profile data in 2018 provided the occasion for the announcement, and consumer Google+ closed in April 2019.
It is the clearest example of a product that a company can install on hundreds of millions of accounts and still fail to make anyone want.
Sources & citations