Narfous
Ugh, I was the first who answered your question correctly and you are being so arrogant with me. I spent my own time to investigate the matter and got you links and info.
Did I say it requires Q2? Haven't you heard of stand-alone mods? Have you heard of TC? Do you realize "mod" is quite a wide term?
SoE definitely has Q2 roots so it is a modification of one kind or another. Yes, it's on Q2E engine, and what's Q2E based on?
As a matter of fact it was enough for me to look at screenshots and see "baseq2" directory in the game to make no mistake about Q2 relation.
I called those games "mods" just for that sole purpose, to stress that they are more like fan-made than commercial titles. Also I was referring to mod community for the same reason.
My message was not supposed to be a start of discussion of what a mod is.
Overlooked you are "THE RIP MAKER" - the plague of all true gamers...
P.S. Alien Arena is a Q2 mod too far. Technically speaking it's a modified Q2 engine's source code based game. As well as SoE is.