It could be very extensible without being written in web technologies. For example, an IDE I worked on was written in C++ with Qt and had an embedded Python interpreter to allow extensions to be written easily. It also provided a .dll/.so extension mechanism for stuff that wanted more performance than Python could give.

It used 10-20 megs of RAM and loaded in about 2 seconds on the computers of the era (about 10-15 years ago).

It wasn't very good, but that's beside the point :-) It wasn't bad because of the technology stack it was built from.