Salem vs Wurm Online
Salem
Salem is an old-school and somewhat obscure (but fun) sandbox MMORPG that unlike Wurm Online has a stronger emphasis on its in-depth crafting system and survival aspect rather than building.Similar to Wurm Online though, Salem is not a voxel-based game, but you are still able to mold the game environment through resource gathering, mining and digging in a way that reminds me of the currently-shelved MMORPG, EverQuest Next: Landmark. Of course, although not exactly the focus of the game, you can still build your homestead and the process is quite similar to Wurm Online except that it occurs at a much higher speed.
Not to mention, the game world in Salem is simply humongous to the point where it feels like an actual world. Salem also borrowed some features from ArcheAge where open-world PvP is the norm, so you'll need to be vigilant at all times, but players who kill and steal for no reason will be labelled as criminals and can be punished.
However, as good as it is despite being an indie MMO and all, Salem does have its fair share of flaws due to its low development budget. So, we'd recommend you to take a look at Salem without carrying along any high expectations. It's a pretty good MMORPG like Minecraft, but if you're expecting a Minecraft clone, you may end up disappointing yourself.
Wurm Online
Wurm Online is a unique sandbox/adventure RPG that many has been touting as being the most realistic one ever. The game is not a solo survival game unlike Minecraft. Instead, you are given the opportunity to build your own settlement - literally from the ground up - and help it to grow. Being an MMO, you can enlist the help of other players to develop your settlement from being little more than a camp with a few shabby and lopsided huts into something that passing bandits might be eyeing hungrily at.There is also an adventure element in this game where you get to venture of into the wilderness to fight a variety of creatures to earn some loot and to level up. Players who enjoy clashing swords with their fellow players can even hop into a PvP world server to enjoy some open world PvP. That said, things will go by a bit slowly if you are playing the game alone though. Wurm Online is an MMO for a reason!
The game has nothing but a fun and great experience to offer to its players and best yet, it's free to play! You can opt for a premium membership if you like just so you can play on multiple servers but, as mentioned, the game can be enjoyed without having to spend a cent.