Frontier: Elite II is a space trading / combat simulation game developed by David Braben and published by GameTek and Konami in 1993. Like in its popular prequel Elite, it features a completely open-ended gameplay without a plot. Instead, you explore space while trading, ferrying passengers, carrying out military missions, engaging in piracy or doing whatever you want. There is no end.
Frontier has been released for Commodore Amiga / Amiga CD32, Atari ST and PC MS-DOS. The PC version was done by Chris Sawyer, who is probably best known for Transport Tycoon and RollerCoaster Tycoon.
This video shows the self-running PC demo version.