Technology

Web browsers

Tor Browser, Firefox

Text message replacements (cross-platform, secure)

Signal, Wire, Telegram

Direct file transfer (secure, no cloud)

OnionShare, Datash, SendSecure, JustBeamIt

File Transfer (secure, temporary cloud)

Tresorit Send, WeTransfer, UploadFiles, FileMail

File sync (no cloud)

SyncThing

Password management (no cloud)

KeePassXC (hint: combine with SyncThing)

Full Cloud
(e.g. google/icloud alternative: email, contacts, calendar, files, etc.)

Disroot, Zoho

File Sharing, Chat, Team Collaboration
(e.g. Slack alternative: private, secure, with cloud)

KeyBase

Secure Email

ProtonMail

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

14 Best Free And Open Source Software For Windows 2018

Open Source Mac

Open Source Windows

11 Best Open-Source Software 2019