Try Caves of Qud, this forum has a thread on it. Its in beta still, but the developer regularly updates the thread with his improvements.
- It's definitely a roguelike.
- It's not a true sandbox. A true sandbox gets boring fast though, like Unreal World. It has an overarching main questline similar to other rpgs. The world is randomly generated with fixed dungeons and towns.
- It's not really survival, unfortunately. It's a post-apocalyptic world where you're required to eat and drink or die. Clean water is used as currency. It's not that hard to survive though.
Try Transcendence. It's a game similar to Escape Velocity Nova, if you've played that. Essentially space action-rpg shooter.
- It is a roguelike in the sense that the galaxy is semi-randomly generated, with fixed space stations guaranteed to show up. Like Nethack's minetown, for example. It is roguelike only in spirit, the fighting is reflex-based.
- It has a little bit of sandbox. I've played the game for days and have not encountered the main plotline. I mined asteroids for hours to get money to buy some decent weapons and armor.
- It's not survival. Unless not getting blown to bits by pirates and hostile aliens counts as survival.
Try Notrium. A action game where you crash land on a hostile planet, starting as either a human, robot, alien, or psychic. All starting classes play completely differently.
- It's not a roguelike
- It's sandbox in the sense that you can do whatever you want. You'll eventually starve or run out of energy of you take too long twiddling your thumbs, though. There are multiple endings, and different endings for the different classes. The human might seek to escape the planet, but the alien might create a new nest...
- It's definitely survival. Survival is what you're trying to do 100% of the time.
Try Space Rangers 2: Reboot. A mostly turn-based space game where you control one pilot trying to turn the tides of a galactic space war against invading robots. There are optional text adventures and RTS battles in optional quests for money and equipment.
- Not a roguelike. Does have an 'Iron Man' option at the beginning of each game, where you are only allowed one save file. If you die the save file is deleted.
- VERY SANDBOX-LIKE. You can fuck off and do nothing and watch the galaxy be destroyed piecemeal by robots. Or you can be a hero and fight the robots tooth and nail. You can be a trader, a pirate, a scavenger. You can be thrown in jail (and suffer a difficult text adventure quest). You can even KILL YOUR OWN ALLIED RANGERS, and receive a dubious 'medal' for it.
- Survival only in the sense that you are fighting for sentient species against hostile AI-robots. You can die from being blown up in your ship, having robots take over a planet that you've parked your ship in, or in many text adventure quests.
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Thinking more on what you want, I don't think you're looking for a sandbox. The term you want is open-world. A sandbox merely puts you in a world with no objectives and that gets boring fast, as you have found. What you want is a world that responds and changes when you do things. Like in Space Rangers 2, if you clear a sector of robots allied forces will come in to defend it, opening up new opportunities. OTOH, if you lose a sector (easily in the hard+ difficulty levels), you will lose the option to trade, refuel, and quest from those sectors.