Grammaropolis is a site made for younger learners and their teachers, but if you want to brush up on your basic grammar, this is one place to do it. You can view some of the information, take some of the quizzes, and play the “Word Sort” game without signing up.
The Nouns section is completely free without signing up. There are explanations, videos, and quizzes. Follow along with the yellow arrows to complete the section.
The other sections have only a limited amount available without signing up. This is from the Interjections section:
There’s also a game on the site: Word Sort asks you to drag the words that fall from the sky into the correct grammar category. Level 1 was very easy, but already from Level 2 there were some words that I think many of my students are unfamiliar with, like the adverb “utterly” and the action verb “hoist”. Level 3 had some interjections like “Congrats!” — informal but very useful.
It looks like there are only 3 levels available without signing up.
If you do want to sign up, it’s $3.99 per month, $19.99 for a year, and $39.99 for a lifetime membership.
There is also an app (both iPhone and Android), which is free but has in-app purchases.
It has the same content as the site, but the Word Sort game is a separate app which costs ¥240, and the Grammaropolis app also links to another punctuation app (¥480).