I have installed Mosquitto on Omega2+. Here is a short description https://wordpress.com/post/omega2blog.wordpress.com/60.
@Claus-Kühnel thanks for your blog! You just might want to edit the link, as it currently points to a wordpress.com login panel, not the blog. Here's the link I figured out actually showing the MQTT post: https://omega2blog.wordpress.com/2017/01/02/using-mqtt-on-onion-omega2/
@luz Thanks for correction.