Instead of typing four capital letters "HEAD", you can say "@" now, e.g. "git log @".

https://github.com/git/git/blob/master/Documentation/RelNotes/1.8.5.txt

試してみた

git log

$ git log -1 @
commit db9bdfbeb044f73a01f6325f4ad61413666a2ce0
Author: Junio C Hamano <gitster@*****.***>
Date:   Fri Oct 18 13:53:05 2013 -0700

    Update draft release notes to 1.8.5

    Signed-off-by: Junio C Hamano <gitster@*****.***>

git rev-parse

$ git rev-parse @~
82c41a9bfc843aa2a6e286bcb917b0436714ebd4
$ git rev-parse @~2
6c2bec96a8215bad7745d559c631e45332c5a9ee

git cat-file

$ git cat-file -p @^{tree}
100644 blob 5e98806c6cc246acef5f539ae191710a0c06ad3f    .gitattributes
100644 blob 66199edd4af6ddcd1398bff13fe9065ba4309a22    .gitignore
100644 blob 11057cbcdf4c9f814189bdbf0a17980825da194c    .mailmap
100644 blob 536e55524db72bd2acf175208aef4f3dfc148d42    COPYING