Line and Skype are my favorites.

Same as Pivren. Also add Snapchat and HelloTalk. If you want to practise on your own, Duolingo is good and a lot of fun.

Line, skype, Facebook messenger, whatsapp.

You can 'chat' online using Skype or a similar medium [Wechat, etc.]. You can write [like this] or speak through a microphone if your computer is fitted with one, or using a mobile phone. You could also exchange [written] messages on this site if you are online at the same time as your correspondent.