Allow users to create posts without logging in?

What you could use to prevent bots filling your site with SPAM:

Post to your blog using email

This functionality used to be in the Core but has since been deprecated.

You can use Post By Email Plugin but that hasn’t been update since 9 years ago.

Or, you can use Post by Mail in Jetpack. Is up to date and maintained by Autommatic (the WordPress guys)

And, you can use Postie Plugin
.

All of these can be found in linked article above.