A simple mod that allows you to download Minecraft worlds from servers
Simply load the chunks you want to download (unloading is fine, the chunks automatically get saved after getting loaded once) and press the keybind to download the world (O by default). This may cause a bit of lag, especially if you're downloading a large part of the world. You can view progress in the logs.
Go to .minecraft and find a folder named "downloaded_world", copy that into the "saves" folder, and play your minecraft world!
Note: You always spawn at 0,0 in the downloaded world, you have to go to the coordinates of the chunks you downloaded (for example you downloaded chunks in 0, 0, -1000, now you have to go to 0, 0, -1000 in the downloaded world to view the downloaded chunks)
This mod doesn't download entities nor container data (like items in chests, furnaces etc...) (maybe in the near future)
this mod requires mcaselector which you can get from here