Próspera is a private charter city and ZEDE (Zone for Employment and Economic Development) on the island of Roatán in Honduras.
The project aims to attract both Hondurans and internationals by (among other things) being business-friendly, having the lowest taxes in the world and having a special legal system where residents can choose much of the legal code that they individually live under.
According to Scott Alexander, Próspera expects 10,000 residents by 2025.
Próspera currently contains only three buildings and has no permanent residents.
Predict the population in 2035 in this related question.