Crafting can function as an end-game but you'd need to put a lot of developmental effort into making that kind of crafting system, which doesn't seem to fit your plan. (Personally I'm not sure why you are putting developmental effort into limited multiplayer...)
Designing a central goal in exploration games without RPG elements.
It seems to me that exploration always has a purpose. Satisfying curiosity can be something that gets things going but the potential for economic gain will most likely be what continues the effort.
With that in mind and considering you want a game with combat elements not present, an idea that comes to my mind is to have the player take the role of a cartographer. I say, put the player in the position of having to draw maps (probably with a sort of tile based paintbrush thing) based on features discovered noting any civilizations discovered, areas that have potential for say mining, agriculture, fishing, or just natural features. The player then sells the maps and is rewarded for accuracy or identifying specific interests. I'm not sure how to handle comparing the accuracy of a player drawn map to the actual world map though.
Alternatively, you could just have missions like, "Identify a potential new hunting ground" or, "Discover a safe route from City A to City B" or for that matter you have to determine if a particular route is safe at all and if not what you might need to make it so.
I like the idea as this project becoming more of a game engine than a standalone title.
Many stories and adventures can be had with it.
You are actually limiting yourself with making it online only with updates.
Think about remaking the Zork trilogy with it. (For practice, of course!)
Very little combat (luck based, pretty much) and no skills to keep track of.
It was a treasure-hunt adventure where the player won when all the treasures were collected.
Puzzles gated the treasures.
Then license out the engine to other devs that would love to make their own first-person adventures.
Of course, this doesn't stop you from making your own stories either...
Go to Amazon. Find a copy of the original Syberia, gameroomswithstyle is who I bought mine from - great customer service, buy it, and play through it.
The Syberia on BFG has been butchered into three parts, so avoid that one.
No levelling up, no combat, pure exploration and problem solving. See also: Nancy Drew - any of them (Ghost Dogs of Moon Lake is a good older one, I haven't played the newer ones yet, working my way through the series. I've heard good things about Castle Malloy), Beyond Atlantis, Mystery Case Files: Dire Grove.
For 'open world' exploration, I recommend X3: Terran Conflict (It's completely stand alone. No need to play the previous X games to enjoy it). There are some plots you can play through if you want, but the universe is there for you to set your own goals and achieve them. Yes, you become more powerful by raising your faction with different races and by buying better ships and more of them or building more factories to give you more money...
The problem you're going to keep running into is that the player needs to see their character improving in some way. That can take the form of mechanical advantages like levels and stat increases, or it can be done with story progression: the feeling that your character is getting closer to 'the goal'. If the player has put hours into the game and has nothing to show for it in terms of his character's 'place in the world', how long do you thing he'll keep running along in that hamster wheel before he gives up and moves on to something else?
It seems like "exploration" on its own isn't strong enough to be the central focus of an entire game.
I just discovered a fishing flash game where you sail around on a boat catching fish. The mechanics of fishing is simple but it drives the exploration. Players want to explore new areas to catch new fishes and sell them to buy equipment to "level up" their boat. I guess I really need a central theme like that so players will continue running the hamster wheel.
I am trying to avoid the easy solution of incorporating the typical RPG combat in my game because I find that it takes a great deal of time and energy to make a good/detailed RPG combat system. Time and energy which I don't have right now.
Well...the game doesn't have combat.
Yeah, you can use the system for non-combat equipment(or abilities) that fit into your game.
The point was to create a bunch of "grinds"(different types of equipment) to keep the player interested,
but the player only needs to do one of those "grinds" in order to progress/compete,
while a player who does them all only has the advantage of switching between different set-ups.
(carefull, if the game is F2P with premium content and you want that content to also not interfere in the
balance of the game, my suggestion could possibly make premium content obsolete for the player)
It seems like "exploration" on its own isn't strong enough to be the central focus of an entire game.
Exploration is a very good focus, you just need to get rid off the RPG idea and add an interesting game mechanism to make it a game (puzzels in this case). Take a look at 3d environment puzzel games. Portal or tomb raider, the latter contains combat, but the main purpose is still solving environment puzzels. Games like Ico or the upcoming game The witness, are nice examples of games which do not contain RPG elements, dont focus on combat at all, are 3d and really successful (or hyped in the case of witness ).
Thanks everyone the input. Really helped a lot in sorting my ideas out. In the end, I decided to try and add some rudimentary combat and RPG elements (equipment, skills etc) into my game.
I realized that games with great exploration tend to have some combat elements in them as the "main" activity. Even a game like Journey had "combat". Pure exploration games like Dear Esther are hard to make for a one man developer with no graphics, and tend to be very short.
You might want to implement a highly visual end goal to work towards. Put a tower on top of a mountain in the middle of the area and challenge the players to find out what's on the top floor. They might need to craft a rope or bridge to cross a chasm, or a ladder to get to the next floor.
To keep things interesting, try to add some environmental storytelling. Let the player stumble across an abandoned encampment and add clues in the surrounding area to let them figure out what happened there. Maybe even "chase" an NPC throughout the area? You could follow tracks, remnants of camp-fires, discarded broken tools..
Another way to hold interest is by using some random events. Have a mysterious creature peer over a bunch of rocks but disappear before the player gets a good look at it. Something makes a noise behind you, but when you turn around there are only tracks. When the player wakes up after a long night's sleep, there's a ritual circle drawn around him.
For this kind of stuff, you could even use the "Lost" method of building intrigue. Just spend an hour thinking up weird unrelated stuff and your audience will spend weeks trying to think of an overarching theory that connects everything.
If you want something to do in a big open 2d grid world, but don't want combat, one thing that can be fun is environmental manipulation to make mobs do things. (So fighting skeletons in Minecraft was meh; what was more fun was luring skeletons from their spawner to my special "skeleton sunroom" to harvest their bones.) If the mobs have deterministic and learnable AI behaviors, and interact with each other and the world, there are lots of puzzles that can arise. (So say you need tiger claws for a kind of medicine. Can you set up the environment so the tiger is led into a poison trap? Or so that he intersects a grizzly's path?)