Chat was the first thing to follow after the creation of the email protocols and clients. 
Originally there was IRC and then that expanded. 


- There is now [IRC OFTC](https://www.oftc.net/WebChat/) (The Open and Free Technology Community) as well, aka WebChat
- Linen is an interesting alternative to chat which incorporates both Discord and Slack messages and also has [forum](https://www.linen.dev/s/linen/c/blog) features. 
- Slack 
- Discord 
- Google Hangouts 
- Whatsapp/Facebook messenger
- Apple iMessage 
- SMS for texting 
- Signal 
- Telegram 
- Line 


Forums: 
- Zulip 
- Discourse 
- Quora 
- Lemmy