Bradley Taylor

This plugin disables the custom fields metabox that WordPress includes by default. The custom fields metabox includes a slow query, which on large sites can take 10+ seconds.
Do not install this plugin if you rely on the custom fields metabox. If you do not know what this means you should probably not install this plugin. If you are using a plugin such as Advanced Custom Fields, Custom Field Suite or similar to manage your custom fields don’t worry – these plugins will be unaffected.
The custom fields metabox performance is currently being discussed in <a href="https://core.trac.wordpress.org/ticket/33885" rel="nofollow ugc">Trac</a>. If you find this plugin useful you may want to follow that ticket.

Remove custom fields metabox

Remove the custom fields metabox to improve performance.

Khanh

(Beta) An extension of Fields, a custom field management plugin. PostLinks provides additional field types such as Series, PhotoLink and PostLink.
Three new field types:
<ul>
<li>PostSeries: link your posts into series and display them with the [series] shortcode, also it comes with 2 widgets</li>
<li>PhotoLink: to be added</li>
<li>PostLink: to be added</li>
</ul>

PostLinks

(Beta) An extension of Fields, a custom field management plugin. PostLinks provides additional field types such as Series, PhotoLink and PostLink.

Remove custom fields metabox vs PostLinks