pEconomy is a simple to use, free economy plugin.
pEconomy has support for Vault, allowing you to use pEconomy with any Vault-compatible economy system.

By default, the plugin will use flat file for storing balances. If you are interested in MongoDB storage, check out the addon.

If you previously used Essentials(X) you can use the balance converter by running the command /peconomy convert essentials. This will convert all Essentials(X) balance profiles.