AstraChat is described as 'standalone and lightweight Jabber (XMPP) client application for mobile and desktop that connects directly to your XMPP server without any proxies in-between' and is an app in the Social & Communications category. There are more than 50 alternatives to AstraChat for a variety of platforms, including Android, iPhone, Mac, Windows and Online / Web-based. The best alternative is Element. It's not free, so if you're looking for a free alternative, you could try Jitsi or Slack. Other great apps like AstraChat are WhatsApp (Free), Pidgin (Free, Open Source), Mattermost (Freemium, Open Source) and Rocket.Chat (Freemium, Open Source).
Element is a secure collaboration and messaging app based on the Matrix protocol. It’s decentralised to deliver digital sovereignty, and based on an open standard for easy connections and interoperability. It is end-to-end encrypted by default.
Jitsi (previously SIP Communicator) is an audio/video and chat communicator with full encryption that supports protocols such as SIP, XMPP/Jabber, ICQ/AIM, Windows Live, Yahoo!, GTalk/Hangouts extensions, as well as OTR, ZRTP, etc.
Slack is a unified communication platform built with an optimized workflow to keep modern teams focused and productive. A familiar chat interface facilitates discussions while advanced features are easily exposed based on context.
WhatsApp is an iPhone and Android messaging app which allows you to exchange messages without having to pay for SMS. In addition to basic messaging WhatsApp users can create groups, send each other unlimited images, video and audio media messages.
Pidgin is an easy to use, multi-protocol chat client client used by millions. Connect to AIM, MSN, Yahoo, XMPP, and more chat networks all at once. It has built-in support for NSS, offering client-to-server message encryption for protocols that support it.
TeamSpeak is a proprietary Voice over IP software that allows users to speak on a chat channel with other users, much like a telephone conference call. A TeamSpeak user will often wear a headset with an integrated microphone.