Litte Snitch

https://www.obdev.at/products/littlesnitch/index.html

And Activity Monitor in the Dock (Icon set to Network Access)

iStat Menus will give you amazing insights on your system in the menu bar. It has a rich choice of views.

There's also Little Snitch for network monitoring.

For the rest, haven't researched much.

Little Snitch -- https://www.obdev.at/products/littlesnitch/index.html