Gregg

This plugin allows you to change the footer text on the bottom left of the admin page.
Once activated, navigate to the Settings -> nuAdmin Footer and change the Footer text/HTML. You can use html to link to your website, your help desk, your email or anything you would like. If you find the plugin to be useful and would like to donate, you can do so in the Settings.
Here’s a link to <a href="http://www.tripleginteractive.com/blog/wordpress/custom-admin-footer/" title="free wordpress plugin: custom admin footer" rel="nofollow ugc">the blog post on this topic</a> for more information. Future version’s will have much more capabilities.

nuAdmin Footer

This plugin allows you to change the footer text on the bottom left of the admin page.

jp2112

Custom Admin Footer Text lets you customize the left and right admin footer text. Overwrite the default text or links with anything of your choosing. Great for developers working on client sites who want to include support links, bylines or credits in the footer.
Currently the left footer says “Thank you for creating with WordPress” and the right footer shows the current WordPress version. For WordPress developers, this is a lost opportunity. Use that space to put links to your website, a copyright statement, whatever you want.
Use it for:
<ul>
<li>Copyright statements/credits</li>
<li>Link to support forum</li>
<li>Link to your other products</li>
</ul>
Or maybe you are just a regular guy who doesn’t like the admin footer. Put a link to your site or whatever you want to see.
<h3>If you need help with this plugin</h3>
If this plugin breaks your site or just flat out does not work, create a thread in the <a href="https://wordpress.org/support/plugin/custom-admin-footer-text" rel="ugc">Support</a> forum with a description of the issue. Make sure you are using the latest version of WordPress and the plugin before reporting issues, to be sure that the issue is with the current version and not with an older version where the issue may have already been fixed.
Please do not use the <a href="https://wordpress.org/support/view/plugin-reviews/custom-admin-footer-text" rel="ugc">Reviews</a> section to report issues or request new features.
<h4>Features</h4>
<ul>
<li>Overwrite existing admin footer text with your own</li>
<li>Disable the plugin and the original text returns</li>
<li>Unclosed HTML tags are automatically fixed</li>
</ul>

Custom Admin Footer Text

Display custom text (or links) in the admin footer.

nuAdmin Footer vs Custom Admin Footer Text