Erfurter Bahn EB (formerly Erfurter Industriebahn EIB) is a private train operator company totally owned by the city council of the city of Erfurt. EB runs passenger services on a large geographical area, but mainly within the state of Thüringen (Thuringia). EB uses RegioShuttle RS1 and Bombardier Itino trains. Although RS1 and Itino now come from different manufacturers, originally they were from one and the same company ADtranz. RS1 was intended to be the one coach version and Itino, earlier referred to as RS2, was its two-coach counterpart. Now the Swiss company Stadler builds and sells RegioShuttle RS1s and has managed to create a real success out of the product. Itinos are today relatively rare.
Picture of three EB RS1 railbuses at Leipzig Hbf 16.7.2018 by Ilkka Siissalo.

A detail of the same train as above. Elster-Saale-Bahn is a marketing trade name of regional express services which EB started in 2012 connecting Thüringen to Sachsen and Sachsen-Anhalt (Saxony and Saxony-Anhalt). This train is serving on the line 22, Leipzig to Probstzella.
Picture of three RS1 railbuses at Leipzig Hbf 16.7.2018 by Ilkka Siissalo.

The Süd-Thüringen-Bahn GmbH is a company owned by Erfurter Bahn and Hessische Landesbahn HLB. STB operates with similar RS1 trains like its mother company EB and their train colours are also almost identical with those of the EB. STB's official headquarters are at EB's offices in Erfurt and the operational center is in Meiningen. This is one of their RegioShuttle RS1 units on an S-Bahn service in Ilmenau.
Picture 2.7.2019 by Ilkka Siissalo.

RS1 railbuses are one coach long and therefore in practical use they are often used as trains with two or more RS1 units coupled together. For this S-Bahn service two RS1 units were used and this is the other one of them.
Picture from Ilmenau 2.7.2019 by Ilkka Siissalo.