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.
Pennywise - Cross-platform application to open any website or media in a floating window
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.
PiP for Mac - Always on top window preview similar to the popular windows only OnTopReplica
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.
PiPer - A DIY Minecraft computer to build gadgets