Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
Standard Notes - A safe place for your notes, thoughts, and life's work
Helium - Helium lets you accept payments by credit card for anything you want to sell online.
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.
X-Mouse Button Control - XMouse Button Control (XMBC) allows you to create application and window specific profiles.