This is intended to be a fun discussion, based on recent news articles and links seen on Hacker News.

https://www.nytimes.com/2017/12/16/us/politics/pentagon-program-ufo-harry-reid.html

https://news.ycombinator.com/item?id=15990480

I'll volunteer one of my experiences first:

A few years ago I saw what looked like a miniature brightly lit moon moving quickly in the daytime sky. It turned out to be a weather balloon reflecting the sunlight, which confirmed by news channels via National Weather Service after numerous other sightings and reports. So, for about 10 minutes many of us saw an unidentified flying object, and then it was an identified flying object.