http://github.com/sgur/unite-everything

everything.vim

" everything source for unite.vim
" Version:     0.0.1
" Last Change: 01 Dec 2010
" Author:      sgur <sgurrr at gmail.com>
" Licence:     The MIT License {{{
"     Permission is hereby granted, free of charge, to any person obtaining a copy
"     of this software and associated documentation files (the "Software"), to deal
"     in the Software without restriction, including without limitation the rights
"     to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
"     copies of the Software, and to permit persons to whom the Software is
"     furnished to do so, subject to the following conditions:
"
"     The above copyright notice and this permission notice shall be included in
"     all copies or substantial portions of the Software.
"
"     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
"     IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
"     FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
"     AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
"     LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
"     OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
"     THE SOFTWARE.
" }}}

" Variables  "{{{
call unite#set_default('g:unite_source_everything_limit', 50)
" search entire path
call unite#set_default('g:unite_source_everything_full_path_search', 1)
" use POSIX regexp
call unite#set_default('g:unite_source_everything_posix_regexp_search', 0)
" sort result by full path string
call unite#set_default('g:unite_source_everything_sort_by_full_path', 0)
"}}}

function! unite#sources#everything#define()"{{{
  return s:source
endfunction"}}}

let s:source = {
			\ 'name' : 'everything',
			\ 'is_volatile' : 1,
			\ 'max_candidates': g:unite_source_everything_limit,
			\}
let s:available_vimproc = globpath(&runtimepath, 'autoload/vimproc.vim') != ''
let s:available_es = unite#is_win() && executable('es.exe')

function! s:source.gather_candidates(args, context)"{{{

	" Win32環境でなおかつ es.exe がなかったら空リストを返す
	if !(s:available_es && s:available_vimproc && vimproc#version() >0)
		return []
	endif

	" 引数文字列がない場合 es.exe は全エントリを表示しようとするので却下
	if len(a:context.input) == 0
		return []
	endif
	
	let l:input = substitute(a:context.input, '^\a\+:\zs\*/', '/', '')

	" vimproc
	let l:res = vimproc#system('es' 
				\ . ' -n ' . g:unite_source_everything_limit
				\ . (g:unite_source_everything_full_path_search > 0 ? ' -p' : '')
				\ . (g:unite_source_everything_posix_regexp_search > 0 ? ' -r' : '')
				\ . (g:unite_source_everything_sort_by_full_path > 0 ? ' -s' : '')
				\ . ' ' . l:input)
	if &shellslash
		let l:res = substitute(l:res, '\\', '/', 'g')
	endif
	let l:candidates = split(l:res, '\r\n\|\r\|\n')
	
	let l:candidates_dir = []
	let l:candidates_file = []
	for l:entry in l:candidates
		let l:dict = { 'word' : l:entry, 'abbr' : l:entry, 'source' : 'everything',
					\ 'action__path' : l:entry,
					\ 'action__directory' : unite#path2directory(l:entry),
					\	}
		if isdirectory(l:entry)
			if l:entry !~ '^\%(/\|\a\+:/\)$'
				let l:dict.abbr .= '/'
			endif
			let l:dict.kind = 'directory'
			call add(l:candidates_dir, l:dict)
		else
			let l:dict.kind = 'file'
			call add(l:candidates_file, l:dict)
		endif
	endfor

	return l:candidates_dir + l:candidates_file
endfunction"}}}

" vim: foldmethod=marker

すばらしいです！
ぜひともリポジトリにしてみてください。

let s:available_es = has('win32') && executable('es.exe')

let s:available_es = (has('win32') || has('win64')) && executable('es.exe')
のほうがいいです。
あと、最新版ではaction__pathのキーを設定しないとエラーになります。
action__directoryも必要です。

あと、この程度ならvimproc#system()を使うべきですね。