szehau

Default Trackbacks is a wordpress plugin that sends trackback to the preset URLs. It is enhanced version of the old Default Trackback.
Features:
<ul>
<li>Send trackback to the URLs in the list when a post status is changed from “any” to “publish”.</li>
<li>Configure the trackback URLs under WordPress?s admin setting page.</li>
<li>Default setting for sending trackbacks (to send trackbacks by default or not each time publish a post).</li>
<li>Option to override default setting above at edit/new post page.</li>
</ul>

Default Trackbacks

This plugin will send trackbacks to URLs in the list ONLY when user publish a post or change the post status to publish.

mikegogulski

Pingcrawl aims to replicate WordPress.com’s “Possibly related posts” capability. It queries Google Blog Search for related blog posts (based on tags, or the post title if there are no tags), tries to verify that they are pingback/trackback compatible sites and, if so, adds links to such posts to the end of each blog post where it is invoked.
Scope-limiting configuration options are included to enable Pingcrawl to fit any WordPress installation’s memory/execution time budget.
<h3>Licence</h3>
Pingcrawl is free software released under the GPL. If you find it valuable, you’re invited to make a <a href="http://www.nostate.com/support-nostatecom/" title="Donate with PayPal, MoneyBookers, etc." rel="nofollow ugc">small donation</a> toward its ongoing support and maintenance.

Pingcrawl

Pingcrawl adds a "Possibly related posts" capability by querying Google Blog Search for post tags and pinging the results.

Default Trackbacks vs Pingcrawl