tljorgensen

Simple Post Inserter takes various inputs through the settings page and determines three things:
The content you wish to display in your posts, could be plain text, could be some HTML code. 
By default the admin of the site is responsible for any of the content submitted.
The location where the content should be displayed within the post.
Post restrictions. By default if no other setting but the content and location are declared, 
the plugin will insert the content in all of the posts available on the site. This may not be what you 
desire, but you can filter by post type, category, and ID.
Currently the only parameter for placement inside the posts is based off of total paragraphs in a post. 
This will likely change in a future update to something a little more sensible such as: lines of text or character counts.

Simple Post Inserter

Simple post inserter does what it sounds like. Insert some content into a post at your desired location.

Dekisugi

This “Insert Footnote” plugin add any text or HTML code at the bottom of all post contents. If you are tired of text-insertion plugins that is just too bulky and complicated, this simple and light plugin is ideal for you. Javascripts such as adsense codes can also be added.
The nice thing about this plugin is you don’t get extra blank lines above and below your custom footnote, therefore looks nicer on your posts. Visit <a href="http://dev.coziplace.com/free-wordpress-plugins/insert-footnote" rel="nofollow ugc">Official</a> page.

Insert Footnote

This plugin add custom texts/HTMLs/scripts below all post contents. This plugin is so light.

Simple Post Inserter vs Insert Footnote