I have a very basic game running right now: using the WASD or arrow keys, the player can move around on a huge empty 2-D grid map. E.g. if you are in the box (0,0), you press the "up" arrow, you end up in box (1,0). The grid lines are there but are invisible to the player. There are some capability for multiplayer interactions: sending each other items (trade perhaps) and messages but not full fledge multiplayer.

I am hoping to design a bare bones exploration game around this. Crucially, there will be NO RPG elements. No EXP, leveling up, combat etc. Currently, I have the player finding materials and combining them to unlock new areas. E.g. finding materials to make a rope to reach a cliff area or building a boat to sail to an island.

However, I am finding it hard to have a central long term goal that the player can strive for without combat. Games usually have RPG/combat elements so players are driven to loot, improve their equipment or level up. This combat driven goal can last forever as new levels or more powerful items can be added to extend the endgame.

Any ideas?

If the game is about exploration, wouldn't the main goal be to explore 100% of the map, including areas that are tricky to get to?

I guess I am hoping to get the player to interact with the environment more and/or get more replay value.

Maybe you're stranded on the island, and the goal is to find someone/something/some information on the island, then escape the island? You could make an achievement for each thing found and each escape route found, so you need to play it differently next time to get more achievements. Various items/materials could have multiple purposes, so you don't need 100% new material for each solution.

No RPG, deserted island, no combat ..... maybe have the player find an old book on the island so he'll have something to read ? :P

What kind of challenges *do* you want the player to overcome ?

Finding and combining items is a nice puzzle, but if that is the only/main challenge for the player i 'd go with Sunandshadow's suggestion and add plenty of NPCs for variety.

Maybe look at some of the later Zelda-games (windwaker ?)

They're not realy RPGs, the player doesn't gain XP and he doesn't outfit skills/equipment to match enemy composure,

but the game does give needed skills/equipment to unlock the next part of the campaign and fight new enemies,

(and only makes the player stronger through increased health which enables the player to not realy having to fight "old" enemies if he runs into them and thus focus more on the new enemies.)

There 's plenty of NPCs as well, and the player has to travel from island to island(windwaker), but some of the islands are uninhabitated as well.

Point being, the game(s) are adventures, but that hasn't stopped the creators from implementing some of the features you wanted to avoid in light-modus.

How about this idea from the incremental game "A Dark Room"?

Later in the game, there is a part where you explore a post apocalyptic wasteland but your food and water supply, and your limited inventory size limits your exploration range.

Unfortunately, this is basically "leveling up", where you level up your water/food/inventory containers.

One of the key issue I have is that as a one-man-no-budget developer, I won't be able to pump out as much exploration content to keep up with players.

I was hoping to add some sort of non-exploration objective and leverage it with the limited multiplayer (find rare materials and trade etc) to keep players hanging around before the next content update.

E.g. with RPG elements, the player can revisit all the areas to grind and level up while waiting for new content.

Maybe implement equipment with levels, where the highest level of equipment is, say, level 10, which will be roughly twice as effective as level 1 equipment.
(fire-armor; negate fire-damage & +1 defense/level, raincoat; negate water-damage, 2 defense & +1 defense/level)
That way players only need to grind a little to get decent equipment, but they can still stay entertained by getting all available types of equipment to level 10.

Maybe implement equipment with levels, where the highest level of equipment is, say, level 10, which will be roughly twice as effective as level 1 equipment.
(fire-armor; negate fire-damage & +1 defense/level, raincoat; negate water-damage, 2 defense & +1 defense/level)
That way players only need to grind a little to get decent equipment, but they can still stay entertained by getting all available types of equipment to level 10.

Well...the game doesn't have combat.

Players explore, pick up items and there is some minor crafting.

After players finish exploring all current content, is there a way to keep them playing? In games with combat, they can just keep leveling up or PvP. But I am finding a hard time designing an "end game" when my game doesn't have combat.