Egosoft's best-selling games X - Beyond The Frontier and it's sequels X-Tension and X2-The Threat are excellent open-ended space combat/trading games.

I'm proud to have played my small part in the X-Universe by creating the X-BTF Strategic Resources web site which has helped hundreds of pilots navigate X-Beyond The Frontier. Not bad considering it only took a long weekend to do it.

Egosoft were so impressed they asked me to write the star-system descriptions for the sequel; X-Tension.
I'm credited under 'additional programmers' or something but all I really did was the system descriptions and some beta-testing.
The descriptions made it into the game with no edits so you can blame me if you have been going mad looking for things that are not there. I offer this quote as consolation..

" A planet is not a world. Planet? A ball of rock. World? A four-dimensional wonder. On a world there must be mysterious mountains. Let there be bottomless lakes peopled with antique monsters. Let there be strange footprints in high snowfields, green ruins in endless jungles, bells beneath the sea, echo valleys and cities of gold. This is the yeast in the planetary crust, without which the imagination of men will not rise." - Terry Pratchett, Strata.

On the bright-side my system descriptions were kept for the third installment X2-The Threat and some of those things now are there. I'll be interested to see if my work made it into the fourth, online, installment which is due soon.

X-BTF Strategic Resources A vital resource for any X-BTF pilot. To help compensate for the lack of a map in the game the 666th Covert Ops Arm have prepared a fully cross-referenced set of system charts with locations of all stations, system descriptions, item and equipment databases, screenshots and more. An offline version is available. Simply download it, unzip it into a directory and open the index.html file in that directory with your browser. It can be viewed with any browser.