Enabled by Deutschlandticket (€49/month unlimited local/regional transit in Germany) & the Italia In Tour ticket (€29/3days unlimited Trenitalia regional trains), I'm planning to spend the next few days traveling from Berlin to Southern Italy entirely on local & regional trains.
I furthermore intend to include urban metro systems wherever feasible/wherever they cross my regional-train path twice; accordingly my journey begins at the U-Bahn platforms of Berlin Alexanderplatz.
Train 1: U2 Berlin Alexanderplatz - Berlin Zoologischer Garten
Depart: 08:43 Arrive: 09:06
Frequency: Every 5 minutes
Operator: BVG (Berliner Verkehrsbetriebe)
Line opened: 1902-1913
Train 2: RE7 Berlin Zoologischer Garten - Dessau Hbf
Depart: 09:20 Arrive: 10:53
Frequency: Every hour
Operator: DB Regio Nordost
Line opened: 1877-1923, electrified 1992
Train 3: RB13 Dessau Hbf - Leipzig Hbf
Depart: 11:11 Arrive: 11:56
Frequency: Every hour
Operator: DB Regio Südost
Line opened: 1857-1859, electrified 1911-1921
Train 4: RE42 Leipzig Hbf - Fürth Hbf
Depart: 12:09 Arrive: 16:11
Frequency: Every 2 hours (supplemented by slower hourly trains)
Operator: DB Regio Bayern
Line opened: 1844-1885, electrified 1939-1942, DDR section de-electrified 1946, re-electrified 1964-1995
Train 5: U1 Fürth Hbf - Nürnberg Hbf
Depart: 16:28 Arrive: 16:44
Frequency: Every 5 minutes
Operator: Verkehrs-Aktiengesellschaft Nürnberg
Line opened: 1835 (first railway in Germany), converted to electrified tramway 1927, converted to metro 1985
Train 6: RE1 Nürnberg Hbf - München Hbf
Depart: 17:10 Arrive: 18:54
Frequency: Every 2 hours
Operator: DB Regio Bayern
Line opened: 1870-2006, electrified 1960-2006
Met up with @Alon in München
Train 7: RE96 München Hbf - Lindau Insel
Depart: 19:54 Arrive: 22:16
Frequency: Every 2 hours (supplemented by slower hourly trains)
Operator: Go-Ahead Bayern
Line opened: 1853-1890, electrified 1968-2021
Train 8: REX1 Lindau Insel - Feldkirch
Depart: 07:55 Arrive: 08:42
Frequency: Every 30-60 minutes
Operator: Österreichische Bundesbahn
Line opened: 1872, electrified 1927-1954
Train 9: S2 Feldkirch - Schaan-Vaduz
Depart: 08:47 Arrive: 09:05
Frequency: Peak only, 11 trains per day
Operator: Österreichische Bundesbahn
Line opened: 1872, electrified 1926
The single-track railway across Liechtenstein is the main route for nonstop intercity Switzerland-Austria trains, so there's not much space for local trains. In 2020 Liechtenstein voters rejected https://vorarlberg.orf.at/stories/3064562/ a referendum to double-track it & expand service.
Verkehr: „Nein“ zum Ausbau der S-Bahn Liechtenstein

Die Liechtensteiner Bevölkerung hat sich am Sonntag bei einer Volksabstimmung gegen den Ausbau der S-Bahn in Liechtenstein entschieden. 62,3 Prozent (10.382 Stimmen) sagten Nein. Mobilitätslandesrat Johannes Rauch (Grüne) bedauert den Ausgang.

ORF.at

@lexande I wonder how hard they negotiate the rail tolls for the through trains.

(But I just checked: the Zurich-Vienna train is slow so I guess Liechtenstein doesn't have much leverage.)

@DiegoBeghin The line is owned by ÖBB; I think Liechtenstein may have given the Austrians a pretty good deal in the 19th century to convince them to route the line that way.