WriteFreely lets you easily group your posts together with hashtags.
Add one at any point in your post, like #this, and it'll automatically be linked to a special page that shows all posts in the blog containing that hashtag. You can also add as many hashtags as you want to your posts, with any kind of capitalization.
NOTE: Hashtags will only auto-link on blog posts, not Draft posts.
If local_timeline is enabled, hashtags are searchable in your instance's reader. All you need to do is add “/t/hashtag” to the instance reader url to find public posts that use that hashtag. Here is an example:
personaljournal.ca/read/t/SingularityNet
Hashtags are also sent to the Fediverse. So if your blog has federation enabled, your tagged blog posts will show up with all the other posts that people have similarly tagged when someone does a search in Mastodon, Pleroma, etc.