I found this thread while trying to find a game like this I had forgotten about. I did get round to finding it by stumbling onto a similar discussion on another board but it highlighted how rubbish searching for such things are even in this day and age.
While I'm here I can add some more to the list now its many years since the threads start.
Overload,The links for DRM free windows,mac and linux demos are in the link below.
https://playoverload.com/playable-teaser/
Minerwars 2081 has a demo on steam, it received criticism for remaining unfinished.
Descent Underground which is under development.
https://www.gog.com/game/descent_underground Sublevel zero redux.
https://www.gog.com/game/sublevel_zero Retrovirus, the game I didn't find as easily as I should have despite knowing it had virus in the name and it was like descent.
A few other games where you could make vessels and fly them around like Descent but being different games over all would be.
Kerbal space program about building and launching spacecraft.
https://www.gog.com/game/kerbal_space_program Orbiter 2016 a free but complex space simulator where you can use or make mods for it.
http://orbit.medphys.ucl.ac.uk/index.html Shattered Horizon wouldn't have sold as well as other games because it forced people to upgrade windows to use the next directx. It also has been removed from steam as of 2014.
FM_James [developer] 27 Aug, 2014 @ 12:46pm
Yes, I am sorry to say that Shattered Horizon is no longer for sale in any region.
As Unbenannte said, we sold our game studio to Rovio in 2012. Futuremark is 100% forcused on making 3DMark and other benchmarks now. We're a small company and can no longer spare the time and people required to support our old game titles.
Since we will not be able to fix the issues with ranking, leaderboards and stats we decided to take the game down from Steam. As someone who worked on Shattered Horizon, it makes me sad to see it go, but it feels like the right thing to do.
If you own Shattered Horizon you can still play single-player and multiplayer on community servers, though stats are no longer being collected. If you have a CD-key from a promotion or gift, you will still be able to redeem it for a copy in Steam.
On behalf of everyone at Futuremark, and the ex-Futuremark Games Studio crew, thank you for buying and enjoying Shattered Horizon. "See you on the flipside."