The Free On-line Dictionary of Computing (30 December 2018):

Z3

    The third computer designed and built by Konrad
   Zuse and the first digital computer to successfully run
   real programs.  The computer was ready in 1941, five years
   before ENIAC.

   Zuse began his work on program-driven calculating machines in
   1935.  His two predessors of the Z3, the Z1 and Z2, were
   unsuccessful mechanical calculating machines.  The Z3 was
   delivered to the Deutsche Versuchsanstalt für Luftfahrt
   (German Experimental Department of Aeronautics) in Berlin and
   was used for deciphering coded messages.  A 1960
   reconstruction of the Z3 is in the Deutsche Museum in Munich.

   The Z3 used about 2600 relays of the kind used in
   telecommunications.  Zuse wrote and implemented the language
   Plankalkül on the Z3.  Programs were punched into cinefilm.

   Zuse built some more computers after World War II, including
   the Z3's successor, the Z4, which was set up at ETH Zurich,
   Switzerland.

   Of the potential rival claimants to the title of first
   programmable computer, Babbage (UK, c1840) planned but was
   not able to build a decimal, programmable machine.
   Atanasoff's ABC, completed in 1942 was a special purpose
   calculator, like those of Pascal (1640) and Leibniz
   (1670).  Eckert and Mauchly's ENIAC (US), as originally
   released in 1946, was programmable only by manual rewiring or,
   in 1948, with switches.  None of these machines was freely
   programmable.  Neither was Turing et al.'s Colossus (UK,
   1943-45).  Aiken's MARK I (1944) was programmable but
   still decimal, without separation of storage and control.

   [Features?  Where was it designed?  Contemporaries?]

   (http://cs.tu-berlin.de/~zuse).

   (http://epemag.com/zuse).

   (2003-10-01)