Pix-Art Messenger is described as 'fork of the Android-App Conversations with some changes, to improve useability' and is a Encrypted Chat app in the security & privacy category. There are more than 10 alternatives to Pix-Art Messenger for a variety of platforms, including Mac, Linux, Android, iPhone and Windows. The best alternative is Jitsi, which is both free and Open Source. Other great apps like Pix-Art Messenger are Tox, Threema, Conversations and Dino.
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.
ChatSecure is a free and open source messaging app that features OTR encryption over XMPP. You can connect to your existing accounts on Facebook or Google, create new accounts on public XMPP servers(including via Tor), or even connect to your own server for extra security.
Kaidan is a simple, user-friendly Jabber/XMPP client providing a modern user interface using Kirigami and QtQuick. The back-end of Kaidan is written in C++ using the QXmpp XMPP client library and Qt 5.