My one of my favorite open source project was Re-think DB!

It was highly light weight real-time DB.
One fine day, I read a blog by the CEO / founder, telling we are under loss since there is no financial support! and we are closing it, by just keeping the website and docs of prev version alive!

I was heartbroken , for days!
This takes the top place for favourite oss project

Btw
It has high no. of stars in github than Mongo db, reddis, etc..