Why not MEGA? While MEGA is free as in beer, the software is proprietary code.

Why not SpiderOak? SpiderOak is proprietary software.

Why not Tarsnap? Tarsnap is partially proprietary and hosts your data on Amazon Web Services.

Ένα πλεγματοειδές δίκτυο είναι ένα αποκεντρωμένο ομότιμο δίκτυο, με συνδέσμους οι οποίοι ελέγχονται από τους χρήστες και συνήθως είναι ασύρματοι.

“Το πλεγματοειδές δίκτυο (τοπολογία) είναι ένας τύπος δικτύωσης όπου κάθε κόμβος πρέπει όχι μόνο να αποθηκεύει και να εκπέμπει τα δικά του δεδομένα, αλλά και να λειτουργεί ως κανάλι για άλλους κόμβους, δηλαδή πρέπει να συνεργάζεται έτσι ώστε να διαχέει τα δεδομένα στο δίκτυο.“

—Wikipedia

Riseup also offers email, XMPP, and chat services, all of which are accessible through Tor Hidden Service addresses. The list of these addresses is available here.

ProtectedText encrypts/decrypts text in the browser, and password (or it's hash) is never sent to the server - so that text can't be decrypted even if requested by authorities.

Use a combination of Tor Browser and a free web browser of your choice to the surf the web.

Try to use Tor Browser as often as possible. Browsing is slower with Tor, but far more secure.

Note: Mozilla Firefox is technically not completely free software, as Mozilla recommends non-free add-ons on their website.

DuckDuckGo is a software-as-a-service (SaaS) hosted around the world that provides you with anonymous search results from these sources. DDG open source components are available here.

There is also a DuckDuckGo hidden service at 3g2upl4pq6kufc4m.onion for Tor users.

MetaGer is a SaaS by the German non-profit SUMA e.V. that provides you with anonymous meta search results.

Startpage is a SaaS hosted in the USA and the Netherlands that provides you with anonymous Google search and image results through a free proxy.