Adam Sewell

The Shopp Lockdown plugin watches for failed transactions on any Shopp payment gateway and limits the transactions to X number of tries.
This comes in handy when gateways like Authorize.Net limits your account after so many failed transactions.
Without this plugin, an attacker could initiate a temporary DoS attack by trying too many fraudulent cards in a short period of time.
This plugin has been tested with Shopp 1.2.x and Shopp 1.3.x

Shopp Lockdown

The Shopp Lockdown plugin watches for failed transactions on any Shopp payment gateway and limits…

itthinx

The plugin protects a site so that only members can access its pages.
Suitable for site lockdowns, private sites and sites that are under construction.
It allows to redirect visitors to a particular page or to the WordPress login.
Members who are logged in have access to the site. 
Members must belong to the site’s Registered group, or to a particular group as determined specifically for the site.
The plugin is an extension to <a href="https://wordpress.org/plugins/groups/" rel="ugc">Groups</a> which is required.
The redirection settings can be adjusted in Settings > Groups Blog Protect :
Redirection options can be set for the blog – or for each blog in a multisite setup:
<ul>
<li>no redirection</li>
<li>redirect to a specific post, note that with this option the blog is shown to the visitor but only that page can be visited</li>
<li>redirect to the WordPress login</li>
</ul>
The redirect status code can be selected among:
<ul>
<li>Moved Permanently (301)</li>
<li>Found (302)</li>
<li>See other (303)</li>
<li>Temporary Redirect (307)</li>
</ul>
Site administrators can determine which group is used to protect the site:
<ul>
<li>By default, users must belong to the Registered group to be able to access the site, so any registered user who is logged in will have access.</li>
<li>The constant <code>GROUPS_BLOG_PROTECT_GROUP</code> can be set in <code>wp-config.php</code> to indicate the name of the group to which users must belong to be able to access the site.</li>
<li>For multisites, the <code>GROUPS_BLOG_PROTECT_GROUP_n</code> constant can be used to indicate the name of the group required to access a particular site, where <code>n</code> is the blog ID of the site.</li>
</ul>

Groups Blog Protect

Protect access to blogs via group memberships powered by Groups.

Shopp Lockdown vs Groups Blog Protect