PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
Helium - Helium lets you accept payments by credit card for anything you want to sell online.
PiPifier - PiPifier is a macOS 10.
Pennywise - Cross-platform application to open any website or media in a floating window
X-Mouse Button Control - XMouse Button Control (XMBC) allows you to create application and window specific profiles.
Afloat - Create beautiful invoices in 3 clicks, without mistakes