PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
Invoice.to - A simple & beautiful invoice generator with Stripe & Paypal
Pennywise - Cross-platform application to open any website or media in a floating window
Free-Invoice.co.za - Free Invoice Software | Free online tool that helps small businesses to generate free invoices and manage their contact list. It can be used as an alternative to expensive invoicing software and online invoicing applications
Afloat - Create beautiful invoices in 3 clicks, without mistakes
Invoice Template - Create beautiful looking invoices in seconds