Class 621 diesel multiple unit - or railbus - of the Greek OSE. This model is one of the newest, being built in 2005 by MAN and HSY. It has lorry or bus engines by MAN of Germany. 15 trains were delivered to Greece and 14 are still in use (?). It's a 1248 kW strong unit used in regional services.
Picture from Thessaloniki 29.11.2015 by Ilkka Siissalo.

A closeup of the same class 621 railbus as above. The text on its bogie says it was manufactured by Bombardier in Germany in 2004. The graffiti is awful and the poor train looks both outside and inside like it hasn't been properly cleaned in years.
Picture from Thessaloniki 29.11.2015 by Ilkka Siissalo.

Another class 621 railbus at the station of Thessaloniki.
Picture 27.11.2018 by Marek Graff.

A sorry sight: Long rows of abandoned passenger coaches and class 620 railbuses left to rot near Thessaloniki main station. The class 620 is/was a two coach railbus with a German MAN engine giving it 1400 kW of power. They were built by Hellenic Shipyards in 1990. 25 trains were built and the latest reports claim that three are still in working condition.
Picture from Thessaloniki 10.6.2016 by Ilkka Siissalo.

A class 620 railbus is literally growing bushes in Thessaloniki.
Picture from Thessaloniki 10.6.2016 by Ilkka Siissalo.

A class 520 diesel multiple unit being serviced at the service depot near Thessaloniki main station. These so called IC2000N, also known as DMU-5, trains were intended for long-haul traffic. 20 trains were built by LEW/AEG in former East Germany 1989-95. All are still in use - at least in theory.
Picture from Thessaloniki 10.6.2016 by Ilkka Siissalo.

A class 520 diesel multiple unit is taking passengers at the Thessaloniki main station. These DMU machines are REALLY noisy.
Picture from Thessaloniki 10.6.2016 by Ilkka Siissalo.

Middle coaches of the same class 520 DMU train as above. It's nice to see at least one coach without the usual all covering graffiti shit.
Picture from Thessaloniki 10.6.2016 by Ilkka Siissalo.

Still the same train as above, but seen from the other side. The class 520 DMU is in practise two diesel locomotives with regular express train coaches in its middle.
Picture from Thessaloniki 10.6.2016 by Ilkka Siissalo.