OneOfOne

This plugin plugin blocks spam in comments automatically, without requiring any end-user input or any javascript.
<ul>
<li>As of version 0.7.7 there’s an option to add an extra javascript check, it’s off by default.</li>
</ul>
In a way it’s similar to webvitaly’s <a href="https://wordpress.org/plugins/anti-spam/" rel="ugc">Anti-Spam</a> however this doesn’t require the user to enter anything at all.
The comment gets marked as spam if any of the following rules are true :
<ul>
<li>If the comment is a trackback.</li>
<li>If the time between loading the page and commenting is less than 10 seconds.</li>
<li>If the Session variable specific to this form is not set.</li>
<li>If the hidden input field have a different value than “-“.</li>
<li>If the comment includes more than 3 urls.</li>
<li>If the referer isn’t set properly.</li>
</ul>
Once the comment gets flagged as spam, and if the auto delete option isn’t set, a json string will be appended to it to show why it was marked, for example :
<pre><code>{ "is-trackback": 0, "no-session-token": 0, "hidden-field": 1, "number-of-urls": 5, "referer": 0, "too-fast": 1.902538061142 } </code></pre>
Translates to :
<ol>
<li>They changed the hidden input field.</li>
<li>They Had 5 URLs in the comment.</li>
<li>It Took 1.9 seconds to submit the comment since the page was loaded.</li>
</ol>
Also note that the time calculations are per-form, so there are no false-positives if the user has multiple pages open on the site and commented on 2 of them in a short period of time.
Feel free to fork it and submit patches / fixes on <a href="https://github.com/OneOfOne/ooo-nospam" rel="nofollow ugc">github</a>

OneOfOne’s NoSpam

Extremely simple, 0 configuration and 0 user/admin-interaction anti-spam plugin.

codetipi

Damn Spam WordPress Plugin
Damn Spam is a lightweight plugin to help clean up that darned spam. This plugin is highly opinionated and, once activated, will automatically send any comments that contain links in the comment body directly to the spam inbox. Granular settings for deeper control will be added over time.
If you’re tired of having to sift through hundreds of comments to find real ones without any links and manually send spammy ones to the spam inbox – then this is the plugin is for you.
<h3>Reporting Bugs</h3>
If you run into any issues, please let us know by <a href="https://github.com/codetipi/damn-spam/issues/new" rel="nofollow ugc">opening up a new issue here</a>.

Damn Spam

Damn Spam is a lightweight anti-spam plugin. Currently highly opinionated - it automatically sends any new comments with links to your spam inbox

OneOfOne’s NoSpam vs Damn Spam