From Wikipedia:
Rich Communication Services (RCS) is a communication protocol standard for instant messaging, primarily for mobile phones, developed and defined by the GSM Association (GSMA). It aims to be a replacement of SMS and MMS on cellular networks with more modern features including high resolution image and video support, typing indicators, file sharing, and improved group chat functionality. As with MMS, mobile service must be activated. Development of RCS began in 2007 but early versions lacked features and interoperability; a new specification named Universal Profile was developed and has been continually rolled out since 2017.
As previously mentioned, HQ images and videos, file uploads, groups chats and more! It supports a lot of stuff, which almost makes it functionally the same as WhatsApp or Messenger. And, unlike Facebook, who develops both WhatsApp and Messenger, there are no shady business practices involved (on a global level, at least – it can vary from carrier to carrier). And even though not ALL features are supported, most of the necessary ones are!
Now here's the best part – ALL Android devices support it, and if you have an iPhone, chances are your carrier does! You can find the full list of carriers that support RCS on Wikipedia.
All messages are end-to-end encrypted, which means only you and the people you are chatting with can read it. Not even your carrier (or Google :D)!
Yes, you got it! It does fck'n rock!