If you type ls<space><tab> into e.g. bash, it will suggest you to autocomplete with all files and directories in the current working directory. On Serenity's Shell, this behavior only occurs after you have entered the first character.
I think this is quite a neat feature, as you can use this to avoid ls a lot, because you know the file you want exists, but you don't remember its name or which character it starts with (maybe you don't know if it's uppercase or lowercase). If you can just press tab, you see all files and folders inside the directory and can then pick.