OK, not necessarily tertiary but certainly secondary:
Education:
GeoGebra (Algebra application). https://www.geogebra.org/
KBruch - (Practicing fractions and percentages)
KTouch - Touch typing tutor
Scratch - MIT programming application
gbrainy - gbrainy is a brain teaser game and trainer to have fun and to keep your brain trained. It includes:
Logic puzzles. Challenge your reasoning and thinking skills.
Mental calculation. Arithmetical operations that test your mental calculation abilities.
Memory trainers. To prove your short term memory.
Verbal analogies. Challenge your verbal attitude.
Use the settings to adjust the difficulty level of the game.
Default is Medium - lower is Easy, higher is Master.
Games with colours can be skipped for users with color vision deficiency (the correct terminology currently used for colorblind users - so the app needs updating!)
Veyon - for monitoring and controlling computers across multiple platforms. (Veyon | Cross-platform computer control and classroom management)
Graphics:
Blender, Darktable, Dia (Technical diagram creation),
E-book viewer, GIMP, Inkscape, Krita, LibreCAD, LibreOffice Draw, Sribus (DTP application)
Office Apps:
LibreOffice, Planner (Gantt Chart creator - Critical Path Analysis), VYM - View Your Mind - Mind map creator, Xournal (Journal).
Programming:
Builder. (Create Apps for Gnome: Apps/Builder - GNOME Wiki!)
Fritzing (Beta): Fritzing
Sysprof. (Start profiling your [computer] system with the Record button.) Apps/Sysprof - GNOME Wiki!
Science:
Avogadro. Advanced molecule editor and visualiser. http://avogadro.cc/
Octave. Powerful mathematics-oriented syntax with built-in 2D/3D plotting and visualisation tools. Drop-in compatible with many Matlab scripts. GNU Octave
KAlgebra. KDE calculator application for Algebra (cf. GeoGebra).
The KDE Education Project - KAlgebra
Kalzium. Superb periodical table application.
KDE Marble - like Google Earth only better - no Google!
Rocs. Graph Theory IDE for designing and analysing graph algorithms. Rocs - KDE Applications
Stellarium. Astronomy application. Stellarium Astronomy Software
Sound and Video:
Ardour 5. https://ardour.org/
Audacity 2.2.1 (the non spyware version) - audio recording software/editor.
KDEnlive - The GNU/Linux Sony Vegas video editor - its what I use for all my Vimeo uploads.
MuseScore 2 - absolutely superb Music notation editor with Instruments so you can make some orchestral movements. Sadly no free tutorials - they have to be paid for!
Pitivi - open source video editor - not as polished as KDEnlive but simpler to use.
xjadeo - XJADEO - The X Jack Video Monitor
I have not listed all the educational apps as the ones I have omitted are for younger learners and applications like VLC and Videos (Video Player) are not educational in themselves, so omitted. I would however look at removing Firefox/Firefox ESR from any version of Zorin as it now grabs telemetry that is hidden (cannot be turned off), probably as a command from their Google sponsors! I would replace with either Epiphany (Gnome) or qupzilla reborn Falkon web browser - if the latter is suitable for children in Africa using Emmabuntus then Falkon should be good elsewhere too! Hope this helps.