CrestaProject

<a href="https://crestaproject.com/downloads/cresta-posts-box/" rel="nofollow ugc">Plugin Homepage & Demo</a>
With Cresta Posts Box you can show, in a single page (posts, pages or custom post types), a small box that allows the reader to go to the next or previous post. The box appears only when the reader finishes reading the current post.
Some features
<ul>
<li>Choose to show next or previous post</li>
<li>Choose the box position (left or right)</li>
<li>Choose the font size</li>
<li>Choose the box width</li>
<li>and more…</li>
</ul>
PRO version features
<ul>
<li>Show Random Post</li>
<li>Show Related Post</li>
<li>Set box background color</li>
<li>Set box text and link color</li>
<li>Set border box and border radius box</li>
<li>5 Animations</li>
<li>and much more…</li>
</ul>

Cresta Posts Box

In free version, you have to chose to show only previous or next post. Too limited to be really useful.

Too poor in free version

Show the next or previous post in a box that appears when the user scrolls to the bottom of a current post.

Kite

Usage:
<ul>
<li>
<code>get_fixed_previous_post( $in_same_term = false, $excluded_terms = '', $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>get_previous_post()</code></li>
</ul>
</li>
<li>
<code>get_fixed_next_post( $in_same_term = false, $excluded_terms = '', $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>get_next_post()</code></li>
</ul>
</li>
<li>
<code>get_fixed_adjacent_post( $in_same_term = false, $excluded_terms = '', $previous = true, $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>get_adjacent_post()</code></li>
</ul>
</li>
<li>
<code>get_fixed_adjacent_post_rel_link( $title = '%title', $in_same_term = false, $excluded_terms = '', $previous = true, $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>get_adjacent_post_rel_link()</code></li>
</ul>
</li>
<li>
<code>fixed_adjacent_posts_rel_link( $title = '%title', $in_same_term = false, $excluded_terms = '', $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>adjacent_posts_rel_link()</code></li>
</ul>
</li>
<li>
<code>fixed_adjacent_posts_rel_link_wp_head()</code>
<ul>
<li>instead of <code>adjacent_posts_rel_link_wp_head()</code></li>
</ul>
</li>
<li>
<code>fixed_next_post_rel_link( $title = '%title', $in_same_term = false, $excluded_terms = '', $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>next_post_rel_link()</code></li>
</ul>
</li>
<li>
<code>fixed_prev_post_rel_link( $title = '%title', $in_same_term = false, $excluded_terms = '', $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>prev_post_rel_link()</code></li>
</ul>
</li>
<li>
<code>get_fixed_previous_post_link( $format = '&laquo; %link', $link = '%title', $in_same_cat = false, $excluded_terms = '', $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>get_previous_post_link()</code></li>
</ul>
</li>
<li>
<code>fixed_previous_post_link( $format = '&laquo; %link', $link = '%title', $in_same_cat = false, $excluded_terms = '', $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>previous_post_link()</code></li>
</ul>
</li>
<li>
<code>get_fixed_next_post_link( $format = '%link &raquo;', $link = '%title', $in_same_cat = false, $excluded_terms = '', $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>get_next_post_link()</code></li>
</ul>
</li>
<li>
<code>fixed_next_post_link( $format = '%link &raquo;', $link = '%title', $in_same_cat = false, $excluded_terms = '', $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>next_post_link()</code></li>
</ul>
</li>
<li>
<code>get_fixed_adjacent_post_link( $format, $link, $in_same_cat = false, $excluded_terms = '', $previous = true, $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>get_adjacent_post_link()</code></li>
</ul>
</li>
<li>
<code>fixed_adjacent_post_link( $format, $link, $in_same_cat = false, $excluded_terms = '', $previous = true, $taxonomy = 'category' )</code>
<ul>
<li>instead of <code>adjacent_post_link()</code></li>
</ul>
</li>
</ul>

Fixed Adjacent Post

Fix the not-excluding terms bug of get_adjacent_post().

Cresta Posts Box vs Fixed Adjacent Post