Scratch is a project mainly written in Vim Script, it's free.
Emacs like scratch buffer
This is a mirror of http://www.vim.org/scripts/script.php?script_id=2107
scratch is a Vim plugin to provide Emacs-like scratch buffer. You can write anything in it, and you can also evaluate a part of the buffer as Vim script. It is a temporary buffer and it is not related to a real file, so the content of the buffer will be discarded when you quit Vim. This buffer is useful when you test a bit of script or other use.
Requirements:
Latest version: http://github.com/kana/vim-scratch
Document in HTML format: http://kana.github.com/config/vim/scratch.html