A bot with a virtual currency members earn and spend — on roles, items or games. Distinct from levelling in that the currency is spendable and can move between members.
The design question that matters is who the house is. A bot that runs games of chance against
its own currency, or sells that currency for real money, has an incentive that is not aligned
with the server.
Every major economy bot gives its games away free; the paid tiers sell configuration and
limits, not access.