NeetoInvoice supports multi-currency invoicing by letting you set a currency for each project. Every invoice created under that project uses the selected currency, so you can bill one client in US dollars and another in euros from the same account.
Agencies and freelancers with international clients use it to invoice each client in the currency they pay in. Choose the currency when you add a new project, or change it later from the project's edit page. You can also record a billing currency on each client record, which keeps client details and invoices aligned.