I've tested countless free ereader apps, and a few stand out for their usability and features. 'Libby' by OverDrive is my top pick—it seamlessly connects with local libraries, letting you borrow ebooks and audiobooks effortlessly. The interface is clean, and the borrowing process feels like magic.
Another favorite is 'Google Play Books,' which supports EPUB and PDF uploads, syncs across devices, and even has a night mode for cozy reading. For manga and light novels, 'Tachiyomi' (Android-only) is a powerhouse with its extensive extensions and customization. 'Kindle' app, while linked to Amazon, offers a robust free reading experience with features like X-Ray and Whispersync. Lastly, 'Moon+ Reader' (Android) is perfect for tech-savvy readers who love tweaking fonts, themes, and scrolling styles.