It's a multi-currency index fund consisting of deposits of currency from users. I think the goal is to make an international currency that would be stable across countries.
The goal I believe is to be 1:1 in multiple currencies (or maybe 0.9:1 or 1.1:1 as close as possible -- so if you were to buy libra with japanese yen it would cost 1:1, or possibly they'd do it based on the highest of the pegged currencies, so if euro is highest they'd go w/ 1:1 euro, then when you cash out to usd directly from libra, you'd go off the current euro:usd differential.
It's definitely complicated, and I think going to be a management / development nightmare. The best thing would've been just go with USD, or Euro since those are the most used funds currently then have a built in forex exchange to instantly change local currencies to libra based on their usd/euro pairing rate.
