Dave

dlb’s Send-A-Link allows visitors to send someone an email containing a link to the post or page.
Key features include:
<ul>
<li>Show visitors a link (icon and/or text) to send an email by adding a function call to your templates or a shortcode to your pages/posts.</li>
<li>The input form, confirmation page, and email message are all based on easily modifiable HTML templates. </li>
<li>Spam protection includes CAPTCHA verification and limiting any given IP address to two messages per minute.</li>
<li>Send-A-Link loads fast because code is compact and does not use jQuery.</li>
<li>Send-A-Link uses Javascript/AJAX for fast, inobtrusive form handling, but it degrades gracefully to provide full functionality to clients without Javascript.</li>
<li>Built and tested on WordPress v3.5.1; although it might work on earlier versions, it has not been tested on them.</li>
</ul>
dlb’s Send-A-Link code is heavily commented, especially regarding WordPress plugin interfaces and AJAX features. This makes it a suitable starting point for novice developers to explore their own programming interests. I have attempted to make the code very understandable. However, I do not claim this to be model code because I am not an experienced developer myself. In fact, I would greatly appreciate constructive criticism.
In the future, I plan to release new versions with the following features, in approximately this order:
<ul>
<li>Privacy reassurance that email addresses are not stored, but IP’s are</li>
<li>Make the “send another message” link consistently re-display form with fields pre-filled</li>
<li>Localize to be ready for translation, including delivery of po and mo files and some instruction on how to use POEDIT to customize the wording, regardless of language. This could especially apply to the error messages.</li>
<li>Attempt to use PHP’s DOM handling routines for more robust and reliable formatting of responses when client does not have Javascript available</li>
<li>Use a stored procedure to flush log daily to reduce number of times it is done</li>
<li>Rewrite using class construction</li>
<li>Add admin screens to specify some things now defined in constants and templates</li>
<li>Make it easy to turn CAPTCHA off or on</li>
<li>Make it easy to use other CAPTCHAs</li>
</ul>

dlb's Send-A-Link

dlb's Send-A-Link allows visitors to send someone an email containing a link to the post or page.

oplugins

wpdevelop

Secure Downloads plugin generate secure download links for protected files and can send emails to your clients for downloading. 
Links can expire after a predefined time, and you can set IP lock for specific download. Download links does not show real location of files at your server. 
You can track every download of files by receiving email about file download with detailed info about download.
<blockquote>
<a href="https://oplugins.com/plugins/secure-downloads/" title="Secure Downloads Homepage" rel="nofollow ugc">Plugin Homepage</a> | <a href="https://oplugins.com/plugins/secure-downloads/#support" title="Support" rel="nofollow ugc">Support</a>
</blockquote>
<h4>FEATURES</h4>
<ul>
<li>Securely distribute your files and track every download.</li>
<li>Upload your files via familiar WP interface.</li>
<li>Define Title, Description and Version Number at “Attachment details” for your protected files</li>
<li>Plugin upload files into secure, protected folder. Website visitors will not have direct access to such files.</li>
<li>Generate secure links to your protected files, which does not show real location of file.</li>
<li>Links can expire after specific time.</li>
<li>Links can be locked to specific IP or IP mask (network).</li>
<li>Configure email template with different parameters.</li>
<li>Send emails to your customers with secure links for download your protected files.</li>
<li>Monitor downloading of each file, by receiving email notification about file download with detailed info about download.</li>
<li>Fast configure your protected files via CSV form. Useful for saving or editing list of files in one form.</li>
<li>Easy reorder list of files via drag and drop interface.</li>
<li>Configure URLs for pages with warning, like “link expired notice”.</li>
<li>Mobile friendly.</li>
</ul>
<h4>SECURE DOWNLOADS IS GREAT FOR</h4>
<ul>
<li>Distribute you files after purchase</li>
<li>Delivery updates of your products to your customers</li>
</ul>

Secure Downloads

Easy generate and distribute secure links for file downloads, that can expire, and track every download.

dlb's Send-A-Link vs Secure Downloads