long bets

Here's another website I'm fond of:
Long Bets

It is an arena for "accountable predictions"

Here is what they say about themselves:

The purpose of Long Bets is to improve long–term thinking. Long Bets is a public arena for enjoyably competitive predictions, of interest to society, with philanthropic money at stake. The Long Now Foundation furnishes the continuity to see even the longest bets through to public resolution. This website provides a forum for discussion about what may be learned from the bets and their eventual outcomes.