Q> Have you used them?
I have used Unity (and hated it). The forum is full of 12yo who get really upset when they're told to look things up for themselves! Also, I didn't like the idea of paying for every little thing that should have been included in the engine to begin with (Shiva3D allows you to export to all supported platforms at no extra cost).
I've also used UE and found it was just too much of a learning curve to be able to get to a reasonable proficiency in a reasonable time.
My main engine before Skyline was Shiva3D which I loved, but couldn't afford to upgrade to 2.0 (I was given a copy of the full version of 1.8 + subsequent upgrades entirely due to the "book" I wrote

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Apart from those, I've used all sorts of other engines over the years (mainly Java & C++ based), and found that most of them were OK for certain projects, but not great for others, hence why I started looking at Ogre (and found out about Skyline!!). Ogre seemed to be perfect for what I wanted as it has an active community, and was free (as were a lot of the extensions).
I've also got a copy of CryEngine, which I had some success with, but again, it took too long to work out how to do things (I don't have that much spare time

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Q> Why have you used them?
I've been programming since the early 80s, so I am always on the lookout for new languages, software etc. I actually enjoy taking things for a test drive, even if I've got no real reason to!!!
Q> What was it that got you to try them, the marketing, website, imagery, videos, tech showcases, GDC conference videos?
As per my previous answer, mostly I've come across them simply by Googling. Though I must admit that CryEngine & UE were both via Social Media!
Q> What do you think skyline lacks that would cause you to use another engine?
AI (such as Steering Behaviours, Formation Motion, Behaviour Trees and Finite State Machines), Multiplayer (this is the main reason I couldn't do much with Shiva3D, as their server was an expensive add-on) & Script Debugging.
Q> What is your opinion and where do you think we should improve or focus that would make you use skyline again?
To be perfectly honest, the main thing that Skyline lacks at the moment is Script Debugging. No matter how easy you make the Scripting, there will always be a need to write a certain amount of code, and Debugging is essential (even for simple things like a comma in the wrong place, a misspelled function, or a colon instead of a semi-colon).
Regards
Shando