EMP is described as 'highly secure messaging system. EMP uses end-to-end crypto, no more breaches, period' and is an app in the Social & Communications category. There are more than 10 alternatives to EMP for a variety of platforms, including Linux, Windows, Mac, BSD and Android. The best alternative is Tox, which is both free and Open Source. Other great apps like EMP are Jami (Free, Open Source), I2P (Free, Open Source), RetroShare (Free, Open Source) and Threema (Paid, Open Source).
Jami (formerly GNU Ring, SFLphone) positions itself as a potential free Skype replacement Open Source and cross-platform. Jami gives you a full control over your communications and an unmatched level of privacy.
RetroShare is a open source cross-platform, private and secure decentralized communication system. It lets you to securely chat, share photos, videos, and more, using OpenPGP to authenticate peers and...
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.
Bitmessage is a P2P communications protocol used to send encrypted messages to another person or to many subscribers. It is decentralized and trustless, meaning that you need-not inherently trust any entities like root certificate authorities.