These are some of the great free and open source software tools available particularly for my friends who live in less free societies. Unless you are a cryptographer, I don’t recommend the Security through Obscurity strategy. Also, consider some of the tools recommended by the Electronic Frontier Foundation (EFF) Surveillance Self-Defense.
- DuckDuckGo - web search without tracking
- GNU Privacy Guard (GPG) - open source version of PGP
- Keybase - site that links social media identities with an encryption key
- Keyserver - MIT’s PGP keyserver (one of many available)
- Mailvelope - browser extension for PGP use in webmail
- Mega - encrypted cloud storage
- OpenVPN - run your own VPN on Windows, OS X, or Linux
- Signal Private Messenger - US-based encrypted SMS, MMS, and voice
- Syncthing - synchronized storage without disk limits using BitTorrent technology
- Termux - terminal for Android devices
- Threema - Swiss-based encrypted SMS and voice
- The TOR Project - a more private method of accessing the Internet
- Wickr - encrypted messaging for iOS, Android, Windows, OS X, and Linux with US government support
For those that just want to work with free and open source software, check out these alternatives to common applications. They are also useful for living a first world lifestyle on a third world salary.
- Libre Office - free replacement for Microsoft Office
- Ubuntu Linux - complete replacement for Windows / running the variant of Ubuntu called Xubuntu enables you to run a modern operating system and applications on minimal hardware such as a 10 year old computer that you can get virtually for free. If you need a graphical interface but want to run at ludicrous speed, check out i3.
- Portable Apps - you can even get by without your own machine or relying on cloud services
- Zotero - organize papers and manage citations
- Hugo - generate static websites that can be hosted anywhere
- Plex - the best media server
- OBS Studio - Open Broadcaster Software Studio
- Muse Score - open source music notation software
- Qubes OS - operating system for those who are tired of repeatedly wiping their system
These are some numerical analysis tools that I find useful. They may or may not be useful for what you do.