In the old TrueCrypt containers you could set an optional second password that would decrypt a different volume. The size of the container file was always the same, a decrypted volume always showed the full container size, the portion not occupied by the data in the main volume was filled with noise, and the data on the non-loaded volume was not protected (so you could erase it without warning by storing too much on the loaded volume), making it practically impossible to prove the existence of a second volume either way in a search situation. I guess there was a reason why the project was stopped.