These are some of the apps I have used over the years, and from those they are the ones that are more focused to work with a general public (whoever does not want to use a Terminal). There is a bias towards using open-source, specially for apps that are just extremely common to use (email, browser, etc). These tend to be ad-free and focused on usability.
Open-source simple apps that are available for Windows and Linux:
- Thunderbird is the mail client that everyone should be using. Besides being open-source(so not snooping in your data) and donation based, it is very average-person friendly. As an adult you probably have 3+ mails on different websites (company, studies, private, spam, etc). This is a hassle to work with if you are using a browser tab for each mail; Thunderbird solves that.
- Redshift is a red light filter (for burning your eyesight less and sleeping better if you look at screens at night).
- Libreoffice is like Microsoft Word (but open-source).
- Chromium is basically Google Chrome (but open-source).
- GIMP is an image editor (like Photoshop, but open-source).
- VLC is a music and video player.
- Kodi is an media-player more useful for when you are watching a series.
- Gparted is a very nice tool for managing your disks/storage/hard drive partitions.
- Gedit is a simple text editor like Notepad.
- Filelight is a way to check how full your disk is and which folder is taking space.
- Texstudio This is a very beginner friendly to use LaTex (format for scientific papers) editor. If you have never heard of LaTex ignore this app.
Non-open source: