Jon Searles' photos with the keyword: 400 ISO,

The rear carriages on some of these trams appear to be unpowered, with the lead unit being articulated, resulting in a total of 10 axles. This system was experimented with in Prague, at least with pairs of T3's (which are non-articulated) pulling unpowered coaches based on them, but ultimately the unpowered trams weren't retained.

In addition to dual-power trolleybuses, Wien also has traditional trams, credited with giving Einstein his ideas on the relativity of time at the speed of light, above it, and below it. These trams are of newer heritage, as you can see from the bogies (trams of Einstein's era were almost always four-wheel and non-bogey), but I know little else about them. Additional information would be welcome, although I may follow up with more research as it is.