Magenta Cuda

This <a href="http://alttypes.wordpress.com/search-types-custom-fields-widget/" rel="nofollow ugc">search widget</a> can search <a href="https://wordpress.org/plugins/types/" rel="ugc">Toolset Types</a> custom posts by the value of Toolset Types custom fields, custom taxonomies and parent/child relationships. It is designed to be used with the Toolset Types plugin and makes use of Toolset Types’ proprietary database format to generate user friendly field names and field values. The widget uses user friendly substitutions for the actual values in the database, e.g. post title is substituted for post id in parent/child fields. The selected posts can be displayed as a standard WordPress list of posts, a spreadsheet of posts with their custom fields or a gallery of featured images.
Version 1.3 supports a <a href="https://alttypes.wordpress.com/#spa" rel="nofollow ugc">single-page application mode</a> where the search results returned by an interactive AJAX request populates a <a href="http://backbonejs.org/" rel="nofollow ugc">Backbone.js</a> collection of models which can be rendered in the same page using <a href="http://underscorejs.org/#template" rel="nofollow ugc">Underscore.js</a> templates and the <a href="http://getbootstrap.com/" rel="nofollow ugc">Bootstrap</a> framework. 
You can view a working sample page using this plugin in single-page application mode at <a href="http://magentacuda.com/demo-of-search-widget-and-wp-rest-server-for-toolset-types/" rel="nofollow ugc">my portfolio website</a>.
<a href="https://alttypes.wordpress.com/#rest-api" rel="nofollow ugc">Version 2.0</a> implements an experimental <a href="http://v2.wp-api.org/" rel="nofollow ugc">WP REST API</a> server for Toolset Types custom post types and custom fields.
Please visit the <a href="http://alttypes.wordpress.com/search-types-custom-fields-widget/" rel="nofollow ugc">online documentation</a> for more details. This plugin works with Toolset Types 2.2.2 and requires at least PHP 5.4. <a href="https://wordpress.org/support/topic/incompatibility-between-my-plugin-and-wpml-multilingual" rel="ugc">This plugin is not compatible with the WordPress Multilingual Plugin by OnTheGoSystems.</a>

Search Widget and WP REST Server for Toolset Types

Search Types custom posts for posts that have user specified values for Types custom fields.

meloniq

Enables searching post meta fields on admin pages.

WP-Admin Search Post Meta

Enables searching post meta fields on admin pages.

Search Widget and WP REST Server for Toolset Types vs WP-Admin Search Post Meta