This free WordPress Plugin allows you the usage of #hashtags and @usernames in your posts
This plugin uses the WordPress Tag system to automatically convert a #hashtag into a Post Tag. Each #hashtag is added as a “normal” tag (without leading hash) to the post, so it is fully compatible with existing tags!
Furthermore this plugin enables you to use @usernames to automatically create links to a users profile page or website and $cashtags to automatically create links to show the current stock value.
You can use #hashtags, @usernames and $cashtags on Posts, on Pages and on Custom Post Types within Content, Title and Excerpt. There are a lot of settings you can customize.