One of many East German tries to make a home computer. KC, standing for Kleincomputer (literally "small computer") was a Z80-based computer expandable by modules. Earlier KC 85/2 had only simple cassette-oriented system in ROM while /3 had also BASIC interpreter. ROM could be expanded by module too: there were assembly language development environments sold as ROM modules as well as FORTH language.
Not only ROM could be added by modules - there were digital input/output modules, RAM expansions or analog/digital (and vice versa) converters. If two module bays were too small, a 4-bay module expander called "Busdriver" could be installed.
KC 85 had some problems. First, the keyboard has been made around very uncomfortable buttons. Keyboard controlling chip, U807D, was eastern clone of SAB3021, a chip made to drive remote controllers. It was good as only two wires were needed to connect a keyboard, but any problem or interference in connection (jack mono plug) resulted in a garbage input. Another problem was with screen modes - there is literally no text mode in KC, everything has to be drawn by copying to IRM (Image Repetition Memory) buffer. It slows down a whole system.
These times orders for computers were so big that these machines were mostly sold to schools, industry or public institutions and were not accessible in a typical market.