SzMake

In English:
No spam in the <a href='https://wordpress.org/plugins/contact-form-7/' rel="ugc">Contact Form 7</a>.Add anti-spambot functionality to the CF7.
It blocks spam without using CAPTCHA,blocked by Invisible internal token-code with ajax.
This plugin blocks 100% of spam post in the author of the environment.
There is no modification of display the contact form.(The added field hidden)
(but the message which is posted by spammers manually via browser is not blocked by this plugin)
This method is the same as the <a href='https://wordpress.org/plugins/sz-comment-filter/' rel="ugc">Sz Comment Filter</a> which is released ahead.
In Japanese:
このプラグインは<a href='https://wordpress.org/plugins/contact-form-7/' rel="ugc">Contact Form 7</a>へのスパムbotからの投稿をブロックするプラグインです。
このプラグインでは、見えない入力欄を用意して投稿時にjavascriptでCAPTCHA入力に変わる固有の確認トークン入力処理をで行うことでスパムBotからの投稿をブロックします。
作者の環境では、今のところこのプラグインで100％スパムBOT投稿がブロックできています。
利用ユーザーのコメントフォームの見え方は変わりません。(追加される入力欄は非表示でユーザーから見えません)
(残念ながらこのプラグインではブラウザを介した手入力によるスパム投稿はブロックできません)
この対策手法は先にリリースしている <a href='https://wordpress.org/plugins/sz-comment-filter/' rel="ugc">Sz Comment Filter</a> と同じ方法です。
<a href="http://wp.szmake.net/contact-from-7-add-spam-bot-filter/" title="Documentation in Japanese" rel="nofollow ugc">日本語の詳細説明ページはこちら</a>
<h4>IMPORTANT NOTE</h4>
This plugin works with ContactForm7 3.6+,or later versions.
This plug-in is not related to the developer of the “Contact Form 7”.
(ja)このプラグインはContact Form 7 バージョン3.6以降との組み合わせで動作します。
(ja)このプラグインの作者はContact Form 7プラグイン開発元とは関係ありません。ご注意下さい。
<h4>Translators</h4>
<ul>
<li>Japanese (ja)</li>
</ul>
<h3>Contact</h3>
email to contact[at]szmake.net
twitter @sxmtz

Contact Form 7 Anti Spambot

No spam in the Contact Form 7.Add anti-spambot functionality to the CF7,it blocks spam without using CAPTCHA.

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.

Contact Form 7 Anti Spambot vs OneOfOne’s NoSpam