I was the CFO of 📝Second Life from 2006 to 2009. I estimate we traded nearly $250m of Linden Dollars to USD on the LindeX during my time (see NBC News, Virtual Fed Chairman Guides Second Life). Second Life was a 📝ledger currency in that for a resident to give a Linden Dollar to another resident, it would be recorded in a ledger by 📝Linden Lab.
A ledger currency is sufficient (in the short term) provided it is managed by an effective, evolving, trusted governance system. Second Life eventually required users to register with its payment services provider (New World Notes, July 2019). Predictable, but I'm surprised it took ten years!
The recently formed (as of early 2020) 📝One Inc Cooperative is developing such a 📝governance system, perhaps as an alternative to the 📝Traditional Silicon Valley Governance System.