Thunderbird is an email, news feed, RSS feed, and chat (XMPP, IRC, Twitter) client. Its features include message management; junk filtering; extensions and themes; standards support: POP,IMAP, LDAP, S/MIME, OpenPGP; file formats supported: mbox, maildir; file linking; HTML code insertion; cross-platform support for Linux, macOS, Windows, with unofficial ports for FreeBSD, OpenBSD; localization; and security. Blog I Forum I Documentation I FAQ
Skype is a telecommunications application that specializes in providing video chat and voice calls between computers, tablets, mobile devices, the Xbox One console, and smartwatches over the Internet. It also allows video calling for 100 people, mobile screen sharing, Skype Number (allows to get a local phone number in another country or region and answer calls on Skype), use Skype to call phones (allows to call landlines and mobiles from anywhere in the world using Skype).