Great Microsoft Windows applications. I don't use Windows enough to remember them off the top of my head.
Too look at
SumatraPDF. Light weight, open-source PDF reader.
Sioyek. Even more light weight PDF reader, oriented around reading research papers and books. Support for "portals", viewing diagrams/etc on another window/monitor.
Everything. Find files and folders by name instantly.
Paint.NET and open-source clone Pinta.