Wordpress - What is the Plural of WordPress?

WordPress is a singular without plural. A second instance would be a fork that could not use the same name, because the name WordPress is a trademark of the WordPress Foundation.

Like Jesus, just more rules.

If WordPress had a plural it would be WordPresses, like in mess or mistress. But the prerequisite for that would be that WordPress becomes either a physical object or self-aware (and able to create self-aware copies). I will update my answer on the day that happens.

Hate to play grammar police here; but using the plural form of WordPress in the example you've given is incorrect.

The correct form would be `...WordPress projects...' not '...WordPresses projects...'

After all you deal with a couple of WordPress projects, not WordPresses projects.

In English, it's an uncountable noun. Like information or advice.

Generally the plural nature is made explicit by the context. E.g. "different versions of WordPress"