Y.Kohno

This is a flexible search form widget. 
You can easily generate a multi condition search form and display anywhere as widget.
複数のカスタムフィールド、投稿タイプ、カテゴリー、タグでの検索が可能な複合検索フォームを簡単作成できるプラグイン。ウィジェットで好きな場所に設置可能。
Currently supports 
– Custom Fields 
– Taxonomies 
– Categories 
– Post tags 
– Post Type

WP Meta Search

Search form for searching through custom fields, post types, categories, tags, and free text.

jphase

WP Modification History enables a metabox that shows modficiation history by date/time, user, and the values that were modified. The modified values are shown in a diff format so that you can easily see what lines and characters were modified, deleted, added, etc.
Within the settings page, you are able to toggle off/on meta values in the event you don’t want certain things to be tracked when hitting the update button on that post type.
Possible future features:
<ul>
<li>Additional settings and display options (AJAX pagination, limit of results per page/metabox, etc.)</li>
<li>Comments and remarks on a particular revision</li>
<li>Email notifications when specific changesets are made</li>
<li>Stats</li>
</ul>

WP Modification History

WordPress Modification History adds a metabox that shows modification history on a particular set of post types.

WP Meta Search vs WP Modification History