FaceTime is a video and audio calling app which comes free with all new Apple devices or can be purchased on older Apple devices.
Microsoft Teams is a communication and collaboration platform that allows you to group chat, run or join audio or video meetings or live events, make calls, store files and integrate with other apps.
Signal is an encrypted private messaging app owned by the Signal Foundation. You can send messages, make audio and video calls, send voice notes, images and videos to your contacts which are secure, untracked and free.
Skype is an audio and video calling app that allows you to video chat, instant message and make voice calls with other people, anywhere in the world, in real time.
Telegram is a secure messaging and audio calling cloud-based app that allows you to send messages, photos, videos and files of any type to your contacts for free.
WeChat is a Chinese platform that is used world-wide. It combines social media posting, chat, messaging, video/voice and payment services in the one platform.