oorja - Your Dedicated Meeting Spaces Online — no installations
Element.io - Secure messaging app with strong end-to-end encryption, advanced group chat privacy settings, secure video calls for teams, encrypted communication using Matrix open network. Riot.im is now Element.
DejaOffice - Super-charged calendar, contacts, tasks and notes apps for Android, iPhone and iPad.
ChatSecure - ChatSecure is a free and open source messaging app that features OTR encryption over XMPP.
Stash - Free Sketch resources, redefined.
Otr.to - A secure peer-to-peer chat in your web browser.