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.

A mesh network is a decentralized peer-to-peer network, with user-controlled physical links that are usually wireless.

“Mesh networking (topology) is a type of networking where each node must not only capture and disseminate its own data, but also serve as a relay for other nodes, that is, it must collaborate to propagate the data in the network.“

—Wikipedia

Riseup also offers email, XMPP, chat and data hosting (via Up1) services, all of which are accessible through Tor Hidden Service addresses. The list of these addresses is available here.

Installing your own add-ons into Tor Browser is not recommended, as they may bypass Tor or otherwise harm your anonymity and privacy. Check the EFF's Panopticlick to see how trackable your browser configuration is by third parties.

If you're using a Firefox-based browser, you can safeguard your browsing habits and stop advertising companies from tracking you by installing uBlock Origin, Request Policy, and HTTPS Everywhere.

Install NoScript and enable ‘Forbid scripts globally’ to improve the security of your browser by preventing 0-day JavaScript attacks. This is a drastic option as it will render many websites unusable as they rely heavily on JavaScript. NoScript offers a whitelist you can use to selectively enable JavaScript for sites you trust, but this is considered especially bad for your anonymity if you're using NoScript with Tor Browser.

Why is Adblock Plus not recommended? Adblock Plus shows “acceptable ads” by default, which works against the purpose of the add-on. Either disable acceptable ads or use uBlock Origin instead.

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.