Haha, I have said it a few different ways myself. Initially, it was pronounced "Extent". Then it was like "ekst" or x'd. Lately I find myself saying E-X-T a lot. My favorite out of the group would probably be x'd.
Jack Slocum
Ext JS Founder
Original author of Ext JS 1, 2 & 3.
Twitter: @jackslocum jack@extjs.com
I used to call it "ekst" but people used to miss the name .... so now I call it E-X-T, being te short name it is, this pronunciation gives it the emphasis it deserves.
Since it's written "Ext" I say it as a word, "ekst". If it were written "EXT" (and especially if it were composed of the first letters of three words) I would pronounce it "E-X-T".