Hashtag WP brings hashtags to WordPress.
Tags are built into WordPress and are used in a way. Hashtag WP makes using tags differently.
You can now tag your post while writing it using hashtags that will be converted to tags when published.
Hashtags are displayed in-content and are ready to be clicked, compared to tags that are seperate from the post and often too far to generate a click.
Just like you do on social networks!