Alex Prokopenko / JustCoded

Just Custom Fields adds ability to extend your Posts, Pages (and other custom post types) and Taxonomies with additional fields. After installation, you will see a simple settings page, which is self-explanatory to use. 
We use the standard WordPress PostMeta API and TaxonomyMeta API to save fields data, so you can use standard WordPress functions in your themes/plugins to get data.
IMPORTANT We do not recommend update plugins on your existing sites from version 2.* to version 3.0+. 
JCF v3.0+ is not compatible with versions 2.*, so some field settings can be lost (and as a result – wrong values on post edit pages).
Plugin supports such field types:
<ul>
<li>Input text</li>
<li>Select Box</li>
<li>Multiple Select Box</li>
<li>Checkbox (single and multiple)</li>
<li>Textarea (you can use WordPress editor too)</li>
<li>Datepicker</li>
<li>Simple Media (files and images upload)</li>
<li>Table</li>
<li>Fields Collection (repeatable fields groups)</li>
<li>Related Content (to set a relation to another Post/Page or Custom Post Type)</li>
</ul>
You can read full documentation on our site: http://justcustomfields.com.
For quick demo you can watch our presentation video: 
https://www.youtube.com/watch?v=7KJeH2d_v48
Starting from v2.0 we have different options to save plugin configuration:
<ul>
<li>Ability to set Fields Settings global if you have MultiSite. So you can set them once, without copying all settings to every new site.</li>
<li>Ability to save Fields Settings to a file system (inside theme or wp-content folder). We expect this option will be popular among the developers. It will be much easier to move your fields’ settings between site versions (dev/production).</li>
</ul>
Starting from v2.2:
<ul>
<li>Simple Media field is now a single file only (before it was multiple). It uses new media upload box from WordPress and saves post thumbnail ID (before it was just a file url). So now you can use the get_the_post_thumbnail() function to work with attachments.</li>
<li>All fields now have “Shortcodes” and hints how to use them inside the templates for non-professional developers.</li>
</ul>
For easy migrations between different sites, we have Export/Import options.
FEEL FREE TO CONTACT ME IF YOU FIND ANY BUGS/ISSUES!
ISSUES TRACKER 
Plugin code is open source and placed in the GitHub public repository. I listed known bugs and future features there. You can post new bugs or feature requests for me there. 
https://github.com/aprokopenko/justcustomfields/issues

Just Custom Fields

Turn WordPress into more powerful CMS by adding advanced and easy to use custom fields

Automattic

Thorsten Ott

Features:
<ul>
<li>simply generate post boxes with multiple fields / groups</li>
<li>easily validate/sanitize input and output data</li>
<li>easy access to field data via $easy_cf->field_id->get() or $easy_cf->field_id->get( NULL, $raw=true );</li>
<li>get error messages for validation failures via admin notices</li>
<li>custom post type aware</li>
<li>extendable to your needs by extending Easy_CF_Field and Easy_CF_Validator classes (see advanced usage)</li>
</ul>
As this script is mainly meant as basis for developers it needs minor coding skills to add this functionality 
to your theme.
In order to make use of this class simply initialize it from the functions.php file of your theme as described below.
<h4>Simple Usage</h4>
<pre><code>require_once( WP_PLUGIN_DIR . '/easy-custom-fields/easy-custom-fields.php' );
$field_data = array (
 'testgroup' => array ( // unique group id
 'fields' => array( // array "fields" with field definitions
 'field1' => array(), // globally unique field id
 'field2' => array(),
 'field3' => array(),
 ),
 ),
);
$easy_cf = new Easy_CF($field_data);
</code></pre>
<h4>Advanced Usage</h4>
<pre><code>require_once( WP_PLUGIN_DIR . '/easy-custom-fields/easy-custom-fields.php' );
$field_data = array (
 'testgroup' => array (
 'fields' => array(
 'field1' => array(),
 'field2' => array(),
 'field3' => array(),
 ),
 ),
 'advanced_testgroup' => array ( // unique group id
 'fields' => array( // array "fields" with field definitions 
 'advanced_field' => array( // globally unique field id
 'label' => 'Advanced Field Description', // Field Label
 'hint' => 'Long Advanced Field description', // A descriptive hint for the field
 'type' => 'textarea', // Custom Field Type (see Ref: field_type)
 'class' => 'aclass', // CSS Wrapper class for the field
 'input_class' => 'theEditor', // CSS class for the input field
 'error_msg' => 'The Advanced Field is wrong' ), // Error message to show when validate fails
 'validate' => 'validatorname', // Custom Validator (see Ref: validator)
 'advanced_email' => array(
 'label' => 'Email',
 'hint' => 'Enter your email',
 'validate' => 'email', )
 ),
 'title' => 'Product Description', // Group Title
 'context' => 'advanced', // context as in https://codex.wordpress.org/Function_Reference/add_meta_box
 'pages' => array( 'post', 'page' ), // pages as in https://codex.wordpress.org/Function_Reference/add_meta_box
 ),
);

if ( !class_exists( "Easy_CF_Validator_Email" ) ) {

 class Easy_CF_Validator_Email extends Easy_CF_Validator {
 public function get( $value='' ) {
 return esc_attr( $value );
 }

 public function set( $value='' ) {
 $value = esc_attr( trim( stripslashes( $value ) ) );
 return $value;
 }

 public function validate( $value='' ) {
 if ( empty( $value ) || is_email( $value ) ) 
 return true;
 else
 return false;
 }
 }
}

if ( !class_exists( "Easy_CF_Field_Textarea" ) ) {
 class Easy_CF_Field_Textarea extends Easy_CF_Field {
 public function print_form() {
 $class = ( empty( $this->_field_data['class'] ) ) ? $this->_field_data['id'] . '_class' : $this->_field_data['class'];
 $input_class = ( empty( $this->_field_data['input_class'] ) ) ? $this->_field_data['id'] . '_input_class' : $this->_field_data['input_class'];

 $id = ( empty( $this->_field_data['id'] ) ) ? $this->_field_data['id'] : $this->_field_data['id'];
 $label = ( empty( $this->_field_data['label'] ) ) ? $this->_field_data['id'] : $this->_field_data['label'];
 $value = $this->get();
 $hint = ( empty( $this->_field_data['hint'] ) ) ? '' : '' . $this->_field_data['hint'] . '';

 $label_format =
 '<div class="%s">'.
 '<label for="%s">%s</label>'.
 '<textarea class="%s" style="width: 100%%;" type="text" name="%s">%s</textarea>'.
 '%s'.
 '</div>';
 printf( $label_format, $class, $id, $label, $input_class, $id, $value, $hint );
 }
 }
}

$easy_cf = new Easy_CF($field_data);
</code></pre>
<h4>Note</h4>
If you’re not using auto_init then meta boxes need to be added individually using 
add_meta_box( $group_id, $group_title, array( &$easy_cf, ‘meta_box_cb’ ), $page, $group_context ); 
and the save methods need to be initialized after adding all meta boxes using 
$easy_cf->add_save_method();

Easy Custom Fields

This is a set of extendable classes to allow easy handling of custom post fields.

Just Custom Fields vs Easy Custom Fields