LINE is a messaging app from LY Corporation offering free chats, calls, stickers and payments, hugely popular in Japan, Thailand, Taiwan and Indonesia, with services beyond chat.
Viber is a messaging and calling app, owned by Rakuten, offering free messages, voice and video calls, communities and business messaging, popular in Eastern Europe and Asia.
Discord is a US chat platform where communities, gamers and friends gather in servers with text, voice and video channels, bots and screen sharing, popular beyond gaming too.
Signal is a privacy-focused, non-profit messaging app offering end-to-end encrypted texts, calls and video, run by the Signal Foundation and widely used by privacy-conscious people.
WhatsApp is a Meta-owned messaging app offering free text, voice and video calls, group chats and file sharing, with end-to-end encryption, used by billions of people worldwide.
Slack is a US workplace messaging platform, owned by Salesforce, organising team conversations into channels and integrating thousands of apps, huddles and workflow automation.