Orbiter Spaceflight Simulator

Orbiter : The Free Spaceflight Simulator is a diamond-hard realistic Simulation Game involving spacecraft and spaceflight in general. It was created by Cambridge tutor Martin Schweiger for educational and entertainment purposes. The simulator has been in development roughly since 2000, and the latest stable version is 2010 P1 (Patch 1), released on August 31, 2010.

Make no mistake, Orbiter is no fast-flyin' laser-shootin' space sim. Think of it rather as Microsoft Flight Simulator meets Planetes.

The game is freeware, so if you feel interested in it and aren't scared by a steeper learning curve, you can grab it here. In addition to this basic game pack, there are literally tons and tons of (equally freeware) fan-made mods that expand the game in virtually every way: Adding new launchers, spacecraft, spaceports and space bases, scenarios and campaigns, texture and graphic updates, even entire planets and solar systems, and new HUDs for the ship's onboard computer... They can be found here, here and here. And don't forget the XR series here!

This game features the following tropes :

 * Absent Aliens: Unless you're counting the mods based on Star Wars, Star Trek, Babylon 5 or other verses, which feature the ships of the various non-human species from those movies and TV shows.
 * Alternate History: In some of the mods and add-ons (e.g. the Soviet Union narrowly beats the US to the first succesful Moon landing, an Apollo Programme-derived spacecraft lands on Mars in 1985, etc.). Also, in the default scenarios Mir is still flying, and has been moved into a convenient orbit for lunar ejections.
 * Asteroid Miners: The Twenty Minutes Into the Future JMC Mining Company in scenarios involving the Delta Glider Mk IV.
 * Better Than It Sounds Video Games
 * Cool Spaceplane: The entire Delta Glider class. And for some, Real Life spaceplanes, like NASA's Space Shuttle, the ill-fated Russian Buran or the never built ESA Hermes space shuttle.
 * Cool Starship / Cool Spacecraft : Way too many to list...
 * Game Mod: The main draw of the game. There are literally thousands, and many of the more high-profile ones are considered by the community to be essential parts of any Orbiter install, to the point that it's just assumed as a given that any new user will have downloaded them.
 * Mohs Scale of Sci Fi Hardness: As hard as humanly possible for a layman-accessible Space Simulation Game.
 * Nintendo Hard: You are, for all intents and purposes, flying a real spacecraft. It's highly recommended that you have at least a basic grasp of orbital physics and the fundamentals of spaceflight before you even think of playing the game.
 * Interplanetary Voyage
 * Like Reality Unless Noted
 * Present Day / Next Sunday AD / Twenty Minutes Into the Future / The Future
 * Really, you can set the date to be whatever you want. Also you can use technology across every era of spaceflight, from early spaceflight technology (the Vostok and Apollo programs) to modern tech (the Space Shuttle and Ariane programs) to speculative tech or tech in research and development (the never-implemented Orion engine, the VASIMR engine, solar sails) to advanced tech from Science Fiction shows and movies (Star Wars, Star Trek, Babylon 5, Stargate, Battlestar Galactica...)
 * Quicksand Box
 * Space Base (of the non-villainous planet surface variety)
 * Space Station: You can even build one!
 * Terraform
 * Wide Open Sandbox

It is also notable for averting these space-related tropes :

 * Artificial Gravity: Unless it's generated by the good old rotation method...
 * Casual Interstellar Travel
 * Conveniently Close Planet
 * Deflector Shields
 * Dramatic Space Drifting
 * Easy Logistics
 * Explosions in Space
 * Explosive Decompression
 * Faster Than Light Travel: The game uses strictly Newtonian physics, not accounting for relativity, so it is theoretically possible for a ship to exceed the speed of light with standard rocket engines. However, the truly ridiculous amount of fuel you would need makes it a practical impossibility. This doesn't count the more fictional mods that DO feature some FTL.
 * Gravity Sucks
 * In Space Everyone Can See Your Face
 * Latex Space Suit
 * No Seat Belts
 * Sci Fi Writers Have No Sense of Scale
 * Space Does Not Work That Way
 * Space Friction
 * Space Is Magic
 * Space Is Noisy: Technically, the core game doesn't come with sounds. The sound addon averts this by default, but gives you the option to play it straight.
 * The sound mod only plays sounds while in cockpit view, in third person view, there's silence (except in atmosphere), aside from the classical music playing.
 * Space Is an Ocean
 * Stealth in Space
 * Streaming Stars
 * Subspace Ansible
 * Two-D Space: Very, very averted.