SpaceSimCentral

Very ambitious game from a single dev and their is a demo which can be downloaded but it is an eye watering 40gb according to steam, so I might have go later on. Space Travellers on Steam (steampowered.com)
From Steam.

About Space Travellers Game
Space Travellers is a unique open-world sandbox space simulator. You have complete freedom of decision and movement. You can travel to familiar places in the Solar System and adjacent systems, or explore over 6000 unexplored distant worlds.

All planets can be landed on and explored. Explore the universe, there are plenty of adventures waiting for you! Travel planets, cities, trade, fight, build factories and bases, colonise. You will also encounter alien life forms and experience many dangers.
History
The year is 2343. War has engulfed virtually the entire known galaxy. The entire free world has banded together to confront the ever-expanding aggressor, formed years ago by the merger of several major multinational corporations into a new state entity: the Holy Empire, headed by the Emperor. After the initial military successes of the Imperium, the forces have gradually become more evenly matched and everything is heading towards a long indecisive war. Until a mysterious new weapon is discovered that threatens the entire planet Earth.
Embark on an odyssey through the universe
Explore the universe, from our Solar System to 6 000 other planets. Discover barren moons and futuristic cities, witness black holes and anomalies as you roam among the stars.



Command spacecraft in thrilling space battles
Embark on lucrative military missions to earn your fortune, or venture to distant planets to hunt exotic creatures and unearth new life forms.



Master interstellar commerce
Forge alliances with over 30 nations and corporations as you build your reputation as a formidable trader. Upgrade your arsenal, sell new materials and earn a fortune.
Shape the universe
Establish thriving colonies and erect factories to sustain your prosperity. Delve into the depths of space to mine both known and mysterious materials.



Experience the universe in your own way

Fly freely in the entire universe
Explore Solar System and 6000 other planets
Land and walk on any planet or star
See black holes and other space anomalies
Visit futuristic cities and bases
Colonize and terraform planets
Build factories to sustain your income
Mine and sell know and unknow materials
Earn money with military missions
Fight in space with hostile vessels
Hunt animals and new life forms on distant planets
Trade with more than 30 nations and corporations
Build your reputation
Buy new space ships and weapons
Create relationships with others

Posted by: @pinback
Very ambitious

You're not wrong! Ticks a lot of boxes, that's for sure!

Been having a bit of play around with the demo and it has promise but it has one big problem in that the UI is very basic, no radar and no way to target anything, although it might be able to do it on the map screen. Also the shields and speed dials etc are on the very far left corner of the screen, not ideal. 
Having had a trawl through the steam forum, it looks like he has been working on the game for two years and he has a scatter gun approach to update, meaning he update what he feels like working on. Fine a free game but not ideal for an early access game where you asking for money. 
The game needs a lot more work on the basics at the moment it feels more like a collection of bits and I'm getting a Limit Theory vide here.

Being playing a bit more the demo and lots of loading screen, some times I thought it had crashed but the game game was just having a bit of think about things.
you can fly straight down to the planets surface and this is the only way to get to a specific target on the surface although their is no real feeling of entering an atmosphere, maybe needs some passing through clouds and some re entry flames.
City seems pretty big with pedestrians and traffic and although their is a taxi missions, theirs not much else to do at the moment.
Probably one to keep an eye on and see if it progressive but the UI needs a lot work.

Games has had an update, 25GB in size some thing to do with the travel in game super cruise mode.

@pinback Had to download a 25GB Demo, then I had to DL a 25GB update!! Over mobile internet!!!

Posted by: @captainkal
@pinback Had to download a 25GB Demo, then I had to DL a 25GB update!! Over mobile internet!!!

I stopped Steam from updating the demo until I think they have made some changes to the UI.

For those that haven't seen the trailer: