Lifted title directly from Softpanorama 
and also as someone who tries various tools one of the favorite site to explore often is alternativeto . I will list some of my favorite software tools.
# Editors
Text editors are very personal, like any personal thing, can start a war
# File Managers
Used all the time, file managers from the OS usually bare minimum, fast and functional. But there are some innovative file managers available.
# Tools and Utilities
Tools and utilities enhance Operating System experience, in CLI world you have so many tools and utilities that you can chain. In GUI world, you will have tools like launchers, alternate shells, search applications.
Window Manager is a software that takes care of your Windows / GUI Frames used by your applications, only if you use Linux as your operating system, there are so many you are spoiled for choices. Here I will list some of my favorites including pseudo ones for Mac and Windows.