Web browsers
Web browser privacy addons/extensions
Text message replacements (cross-platform, secure)
Team chat, voice, and video conferencing (Slack alternatives)
Element (formerly called Vector and Riot), Discord, KeyBase
Direct file transfer (secure, no cloud)
OnionShare, Datash, SendSecure, JustBeamIt, ToffeeShare
File Transfer (local network only, no cloud)
File Transfer (secure, temporary cloud)
Tresorit Send, WeTransfer, UploadFiles, FileMail, file.io
File sync (no cloud)
Password management (no cloud)
KeePassXC (hint: combine with SyncThing)
Full Cloud
(e.g. google/icloud alternative: email, contacts, calendar, files, etc.)
Full Cloud (self hosted)
Secure Email
VPN (Virtual Private Network)
ProtonVPN (free & paid), NordVPN (paid & good)
Free Office Suite (Microsoft Office Alternative)
LibreOffice (better MS compatibility), OpenOffice
More free and open source source software