Not really an app and not really dutch, but since the first actual version I saw came from Jan's keyboard, there it is.
It's a holy mess of a protocol for transfer of medical data. It's text, delimited by carriage return, fields separated with carets (aka circumflexes) and pipes, with a lead field being a TLA denoting the type of the record and the semantics of the fields in the rest of the row. So one row can mean one thing, next one something quite different.
I saw it first some time in 1987 or so, when I was cooperating with Mika Fišer on those articles. He took me to antituberkulozni dispanzer, where his dad was the manager (and actually the founder), where they had some analyzer of something (blood? EKG? dunno), which was actually a computer, with a 6502 (or was it 6205?) processor, yup, the same kind as in the Commodore 64. It was saving its findings in files on a 5,25" floppy, and he showed me those files. All those TLAs and bunch of ^^|A^^23^Z^ etc etc.
Feds, being a medical app, couldn't avoid this mess. Thirty-some years later, it's neither standardized nor made easier. Basically, the manufacturers of such machines don't give much of a damn about programming, and the programmers don't know enough medicine to talk with them, so the mess has only grown more complicated. The standard as described above still stands, but the devil in the details is a different one for each manufacturer and each machine and each type of record. It gets easier only when it's used as a means of communication between two apps, and the programmers actually talk.
It's one bullet that I avoided, as I never had to deal with it. Jan did nominate me for the task at some point, but by the time I finished what I was doing then, something more urgent came up so I switched to that, and this came to Nina, who kept at it for a few years. I even created a version of upFeds for the little app, so she'd have less trouble with distribution of new versions.
There was some talk of even LI being switched to HL7, but now with two of us out of the picture, I don't see it happening anytime soon.