Yomimono is an online textbook with the goal of teaching you everything you need in order to be able to read Japanese.
Yomimono provides free lesson modules available for beginners to get started learning kana, kanji, vocabulary, and grammar concepts.
Each lesson module starts off with kanji, moves onto vocabulary that uses the kanji, and then grammar with example sentences that use the vocabulary. With this ordering, you're given opportunities to gradually learn things while reinforcing your newly-learned knowledge. The interface is simple, and the explanations for grammar are fairly easy to understand. The volume of each module is not too overwhelming, either. At the end of each lesson, you get to quiz and review what you learned in the module as well.