I have a special spreadsheet for study tools. Here are some of my favorites.
I agree with @Kimberly-Mandarin-HSK_4. Skritter is by far the most useful tool to review characters but also quite expensive (there are other newer alternatives like TofuLearn and Inkstone if that is an issue). If you don’t care about writing at all, Hack Chinese is perfect.
I have originally learned how to memorize characters by following the methods (storytelling and memory palaces) outlined in this book: Learning Chinese Characters. The other tool I use daily is the Outlier Dictionary for Pleco that breaks down each character for you so you can memorize it. Thanks to these strategies (and daily Skritter practice) I’m now able to read at HSK4/5 level.
For reading, my Preply tutor and I have been using HSK Reading. Like others, I also try to read graded readers daily - for HSK4 I highly recommend Journey to the West by Jeff Pepper. There are many other books by this author for all HSK levels and even free audio versions of these books.
If you’re preparing for HSK (or if you just want to improve your grammar), the two best resources I found is the Chinese Grammar Wiki and Chinese Zero to Hero (I purchased the Ultimate bundle and it’s absolutely worth it. They also have a few free courses).
Speechling is great for practicing listening and pronunciation. You can get free feedback on 10 recordings every month. If that’s not enough or you just want an immediate feedback, you can also try this free Pronunciation Training tool written by yours truly. Currently it supports Chinese and Japanese 