Resilio Sync: https://www.resilio.com/individuals/ Uses Bit Torrent protocol to sync folders between two or more computers (and mobile devices). GREAT thing to have! I use it to sync my entire Documents and Desktop between office and laptop computers. It also has an archive so can recover deleted files.
Evernote: https://evernote.com/why-evernote Note taking, cloud-based storage.
Zotero: https://www.zotero.org/ If you write research papers with lots of references, this is awesome. It stores all your references, captures references from websites, and organizes bibliographies. Plugs into OpenOffice Writer/Word
LibreOffice: https://www.libreoffice.org/ Free office suite replacement for MS Word/PowerPoint/Excel
Gimp: https://www.gimp.org/ Open source alternative to Photoshop
Inkscape: https://inkscape.org/en/ Open source alternative to Adobe Illustrator (vector graphics)
Python, Jupyter, iPython http://ipython.org/ Python replacement for MatLab.