Eurail Pass Explained
In general the Eurail pass is valid on train lines only. Metropolitan public transport is usually not included in such rail-passes. The Man in Seat 61 says:
Railpasses cover all the trains run by the main national train operator in each country covered by the pass, including local trains, suburban trains, regional trains, inter-city trains & international trains. [...]
Railpasses don't cover city metro/underground/subway trains, trams or buses as these are usually run by urban transport authorities, not by the national rail operator.
Having said this, note that Eurail has a page listing benefits per country. From there you can gather all the information required for your trip. All in all, it's up to you to figure out if this is a viable option, depending on your itinerary and budget.
Benefits in Germany
To give you a few examples, the benefits for Germany include travelling on S-Bahn trains:
Hop on the S-Bahn and discover major German cities
A Eurail pass is also valid on the S-Bahn (suburban metro railways) networks that DB operates in major German cities. The S-Bahn can be recognized by its logo (a white S on a green background)
S-Bahn Validity in Berlin
Others have mentioned that the pass isn't valid on Berlin's S-Bahn. I coulndn't find any mention of this, but I welcome edits. The Eurail webpage for Germany however says that the pass is indeed valid on the S-Bahn, and it mentions a station in Berlin:
Your Eurail pass is also valid on the S-bahn rapid transit system. Take the S-Bahn to Bahnhof Potsdamer Platz for the panoramic observation deck.
Moreover, this post on a related thread from Rick Steves' dating December 2014 says that the Eurail pass should be valid for the Berlin S-Bahn routes:
The Eurail pass includes all S-Bahn that are run by German Rail. That might now include all; at one time there was a line in Berlin that was not included.
Benefits in Austria
The same benefit seems to apply to Austria. Indeed the Eurail pass allows to travel for free on the S-Bahn in Vienna and Innsbruck:
Get free transportation on the S-Bahn
Eurail pass holder can travel for free on the S-Bahn in Vienna and Innsbruck.
Benefits in France and Italy
The benefit pages for France and Italy however mention nothing of the like.