Add Papercups to Custom communication systems

README.md

@@ -297,6 +297,7 @@ _CalDAV or CardDAV web-based clients._
 - [Mumble](http://wiki.mumble.info/wiki/Main_Page) - Low-latency, high quality voice/text chat software. ([Source Code](https://github.com/mumble-voip/mumble), [Clients](https://wiki.mumble.info/wiki/3rd_Party_Applications)) `BSD-3-Clause` `C++`
 - [Node-Chat](https://github.com/IgorAntun/node-chat) - Not-so-basic open-source chat with admin features. `MIT` `Nodejs`
 - [OTS](https://ots.fyi/) - One-Time-Secret sharing platform with a symmetric 256bit AES encryption in the browser. ([Source Code](https://github.com/Luzifer/ots)) `Apache-2.0` `Go`
+- [Papercups](https://papercups.io/) - An open source live customer chat web app written in Elixir. ([Demo](https://app.papercups.io/demo), [Source Code](https://github.com/papercups-io/papercups)) `MIT` `Elixir`
 - [PushBits](https://github.com/eikendev/pushbits) - Self-hosted notification server for relaying push notifications via Matrix, similar to PushBullet and Gotify. `ISC` `Go`
 - [Rallly](http://rallly.co) - Rallly is a free collaborative scheduling service. ([Source Code](https://github.com/lukevella/Rallly)) `CC-BY-SA-4.0` `Nodejs`
 - [RetroShare](http://retroshare.org) - Secured and decentralized communication system. Offers decentralized chat, forums, messaging, file transfer. ([Source Code](https://github.com/RetroShare/RetroShare)) `GPL-2.0` `С++`