Yes, the "electric" GUI was incredibly fast and effective. The K2 GUI was basically the only GUI system I've ever used in which it is easier to write a GUI for a simple system than a batch command line. It looks basic and wouldn't have won any design awards, but it was crazy fast and crazy effective. See e.g. The S- spreadsheet (copied here in its entirety), see near the bottom of http://nsl.com/papers/spreadsheet.htm for screenshots and discussions

    S..t:".[`D;(;);{. y};S[]];S[.;`f]:9$D[]"
    S:D:.+(`a`b`c`d;4 6#,"")

Other examples: http://nsl.com/papers/puzzle15.htm , http://nsl.com/papers/calculator.htm

I suspect the reasons it was removed were:

(a) it was a lot to maintain compared to the rest of the k environment, as it needed to be implemented for all systems independently (X, Win, Mac at the time), and introduced dependencies that were about 10x larger than the base system.

(b) it wasn't actually a selling point - being simple and local GUI meant that while it was nice for the programmer users, it wasn't useful for end users, who usually had no K license of their own, and who expected everything to be web-able and importable to Excel.

(c) it wasn't extendable with more widgets. Needed a small HTML control or video player in your GUI? touch luck.

I believe the GUI idea is still alive, but today it can be web-based. See 1010data.com.

1010data's web UI isn't actually based on the K2-era GUI framework; it is architected as a reasonably conventional web application that happens to use K3 as a server-side language. The 1010data query language offers facilities for making data-driven UIs for interactive reports and the like, but any semantic similarity to the K2 GUI system is probably coincidental.

>any semantic similarity to the K2 GUI system is probably coincidental.

Hardly coincidental! I very much had the K gui in mind when I originally architected it (and I'm not sure I'd describe it as a "reasonably conventional web application"...)

So 1010data's purpose is to sell analytics tools to kdb+ users? Does kdb+ not come with a simple way to pipe output to a chart? For the price, I'd hope they had something more than a REPL.

1010data's analytics tools and database are entirely their own product, developed separately from kdb+. While these are implemented in K (K3, which precedes kdb+/q/K4), the end users are not K programmers any more than WordPress users are PHP programmers.