Mosquitto is a message broker that implements the MQ Telemetry Transport protocol version 3. MQTT provides a lightweight method of carrying out messaging using a publish/subscribe model.
What should the average user do with these packages: At this moment, nothing. Don't bother installing them. This announcement is targeted more towards developers.
a proxy server is a server (a computer system or an application) that acts as an intermediary for requests from clients seeking resources from other servers.
"Dial out": the call is placed by calling your Google VoiceMail, and asking it to place the out-going call. "Dial Back": The Google Voice website is contacted, and it is asked to place the call. GV website first calls you and then calls the out-going number. And then it connects the two. "Dial Back" requires a data connection and a voice connection, while "Dial Out" only needs a voice connection.