ericjuden

This plugin allows you to use $_COOKIE, $_SERVER, $_SESSION, $_GET, $_POST and $_REQUEST data in a Gravity Form through the merge tags of a field. I’ve only really tested this using a hidden field.

Gravity Forms Extended Merge Tags

It's amazing how few people seem to know about this plugin. Incredibly simple, but also really helpful when using $_SESSION variables to track website visitors.
I use it to get referring website data, so I can easily store it in a $__SESSION variable. Then when the visitor fills out a Gravity Form, I can pass along the stored vars.
I crafted a Lead Source Tracking for Salesforce script that uses this plugin to pass along the details to Salesforce when a form is submitted.



Brilliantly simple

This plugin allows you to use $_COOKIE, $_SERVER, $_SESSION, $_GET, $_POST and $_REQUEST data in a Gravity Form through the merge tags of a field.

tronhammer

This plugin will mimic a keep-alive ping by utilizing jQuery to perform an ajax request to the current page, which will update 
the session token tied to PilotPress and or any other system attached using PHP built in sessions. Session Slap will also provide 
a settings interface to allow admins to configure details relating to interval amount (which is defauled to 5 minutes less than the 
session.maxlifetime set in php.ini).
A few notes about the sections above:
<ul>
<li>Configuration options are available in the Settings -> Session Slap menu.</li>
<li>Updates built in PHP sessions only.</li>
<li>Attempts to access session.maxlifetime ini settings, but will default to 24 minutes if not available.</li>
</ul>

Session Slap

Session Slap mimics a keepalive ping by making an AJAX request to the current page to refresh active session timestamp.

Gravity Forms Extended Merge Tags vs Session Slap