Here is a description how to create a working Wrapper for Mac OSX until a native version is availlable. I tried it and it works.

Preparations

- Download, install and run Wineskin Winery

Create the wrapper

- Click "Update" and then "OK".

- Click on the small circular arrow button.

- Click on the small "+" button next to "New Engine(s) available".

- Select WS9Wine1.7.0x and click "Download and Install" and "OK".

- Click "Create New Blank Wrapper". Name it as you like (e.g. "Terraria" or "Steam").

- Click "Cancel" when asked about Gecko.

- Click "View Wrapper in Finder"

- Quit Wineskin Winery.

Installing the Game

- Rightcklick on wrapper and choose "show package contents"

- Open Wineskin

- Click "Choose Setup Executable"

- Search for the install.exe and install as usual

There may be some errors during installation but you can ignore them and klick on OK.

Install .NET

- Click on "Advanced", "Tools", "Winetricks".

- Search for "msxml3", click the disclosure triangle next to "dlls" and check the box next to "msxml3". Click "Run", then "Run" in the window that pops up.

- Winetricks will open Cnet in a browser. Click "Download now" to get MSXML 3.0 SP7.

- Close the browser.

- Open Finder, locate the downloaded file "msxml3.msi" and move it to "/Users/*Username*/.cache/winetricks/msxml3".

- Go back to Winetricks, then search for, check and run "msxml3" again.

- In the MSXML installer, click "Next", "I accept...", "Next", "Next" (you don't have to enter your name), "Install" and "Finish".

- Back in Winetricks, search for, check and run "dotnet40".

- In the .NET 4.0 installer window, check the first checkbox, click "Install" and "Finish".

- Close the Winetricks window and quit the wrapper.

Run the game by doubleclicking on the wrapper.

Thanks, I didn't know about msxml3.dll, so the .Net- and XNA installers kept crashing. It works great now.

There is a little thing to add though: the default save location is under ~/Documents, which should be a massive no-go for developers, but common malpractice on Windows. We can fix this easily: In Wineskin under Advanced -> Options -> Modify Mappings we can set the path. I prefer the following for the Documents folder:

$HOME/Library/Application Support/GOG.com/Terraria/Documents

Same for the other folders, but they are not important. The Application Support directory is where save files should usually go and the "GOG.com" subdirectory is where GOG games save to usually, so it's all in one place now.

Thanks for the addition. ;)

Good to hear! I imagine this would run well on Linux, too? In the past I looked at running this game but it looked like such a pain in the ass... plus I don't like steam much.

Since these are steam-less files, could this game potentially be played via mono's runtime environment? There are not many games I wish had a nice, native port (read: .net-less) for Mac/Linux, and this is one of them.

There is no reason this shouldn't work on Linux with Wine if you know how to use it. The critical parts are that you execute the Winetricks (msxml3 and dotnet40).

The game uses Microsoft's XNA framework, so Mono alone isn't enough. As far as I understand the open-source alternative to XNA is MonoGame:
http://www.monogame.net

I don't know how, but it someone could install the framework Terraria might run natively. At least as natively as a .NET/Mono application can.

EDIT Here is a video in action:
https://www.youtube.com/watch?v=cpK9ZQFRa3o

Sadly people never explain how they got it to work, so every pre-made solution I tried has not been working for me. i think Wine is going to be the simplest solution until we get official Mac- and Linux ports. They are coming, but there is no release date yet.
http://terraria.org/news/terraria-for-mac-linux-in-development

Hello, does this work for multiplayer also?

EDIT:

So, i've managed to make the game work... thanks for that :).
No luck with the multiplayer part tho.
Is there a solution for this?

I haven't tried the multiplayer et, but maybe you'll have more luck trying to join a game rather than hosting it? Things can be weird sometimes.