tModLoader is essentially a mod for Terraria that provides a way to load your own mods without having to work directly with Terraria's source code itself. This means you can easily make mods that are compatible with other people's mods and save yourself the trouble of having to decompile then recompile Terraria.exe. It is made to work for Terraria 1.3.
tModLoader saves worlds and players separately from vanilla worlds and players. Vanilla worlds and players can be ported to tModLoader worlds and players simply by copying over save files, but tModLoader worlds and players can be ported back to vanilla worlds and players only if they do not contain anything modded.
My goal for tModLoader it to make it simple as possible while giving the modder powerful control over the game. It is designed in a way as to minimize the effort required for me to update to future Terraria versions. Once I make substantial progress on tModLoader, I will also become open to everyone's suggestions for more hooks.
Download and installation instructions are on the forums thread.
Note that this repository will usually be ahead of the current released version.
Huge thanks to ChickenBones for creating the code patcher!
If you want to contribute to this project, you'll have to download the code for tModLoader, including all the changes made to the Terraria source. This requires you to have purchased your own Terraria.exe first. In order to do get the tModLoader code, first clone the repository, then run the setup.bat file. If setup.bat doesn't work, you may have to unblock the files in the repository. Once tModLoader Dev Setup is open, just click on the Setup button and select the location of your vanilla Terraria.exe. Warning: decompiling will probably freeze your computer for a couple of hours. So you'll need to find something to do in real life until that's done.
When that's all done, you should have the tModLoader source in the src folder. Open the solutions folder then open the tModLoader solution.
So you've made some changes to Terraria and want to commit them. Run setup.bat again, then (Important) click on Format Code. Select the src/tModLoader folder, then wait a bit for it to format. When that's done, click on Diff tModLoader. This will create patch files with the changes you've made. Finally, all you'll need to do is commit the patches folder.