Saber

Not as in a sword, but as in the Spanish/Portguese infinitive "to know."

This is a really fascinating example of a complementary currency. The idea is that you hand out these special banknotes to seven-year-olds. They're valuable only in that they can be used to pay university tuition.

You're probably thinking that the idea is for the seven-year-olds to hoard them until they go to college, but that's not it at all. Instead, the idea is to encourage older students to tutor the younger students in exchange for the currency. In fact hoarding is strongly discouraged by making the currency demur at 20% per year.

From what little I've read, it works quite well: giving university students a $1 billion discount in exchange for about $10 billion worth of teaching.