Company stands for "complete anything" and is a modular in-buffer completion mechanism.
Watch the screencast.
Company comes with many back-ends, e.g. `company-elisp'. These are distributed in individual files and can be used individually.
Place company.el and the back-ends you want to use in a directory and add the following to your .emacs:
(add-to-list 'load-path "/path/to/company") (autoload 'company-mode "company" nil t)
Enable company-mode with M-x company-mode. Completion will start automatically after you type a few letters. Use M-n, M-p, <tab> and <tab> to complete. Search through the completions with C-s, C-r and C-o.
Also available via ELPA.
If you have any feedback, please email me, or visit this package's page at the Emacs wiki.