I've tried many tools--books, websites, applications--over the course of my short time studying Japanese. The following is a partial list of Japanese learning tools I've tried in the past, but that didn't work for me.
This isn't to say any of these tools are bad. In fact, I know many people have used them to great effect. However, I found they did not benefit me--at least, they have not so far.
Tools I've Tried
Even more so than the other things on this list--or on my list original list of things that do work for me--Anki seems to be ubiquitous among online learners of Japanese.
And for good reason. It's an excellent flash card application, which is vital to learning vocabulary, if nothing else.
The SRS system in both of those tools makes more sense to me, and the fact that they both require actual input seems to make them work better at helping me actually remember items.
There are ways of heavily customizing Anki to have it work exactly how you want it to, but I've never explored those--Houhou does 95% of what I want out of the box, and getting it to 100% was just a matter of copying and editing a couple of extremely simple XML files.
It's certainly possible I'll use Anki again in the future, for things that Houhou doesn't handle well.
Genki was (and is) recommended basically everywhere you see people discuss Japanese textbooks.
A lot of Genki also seems designed for people in a classroom setting--or at least people learning with others. Since I'm a solo learner, most of that was useless to me.
My problems with Genki are 100% personal. If you're looking for a Japanese textbook, Genki may well work perfectly for you, as it has for many others (based on the recommendations I see.) It seems unlikely I'll be coming back to Genki, however.
iKnow.jp is a very nice SRS vocabulary site. It is subscription-based, though there is also a free trial.
Similar to Anki, Wankikani and Houhou ruined me for iKnow. It's a fine system, though I don't fully understand the SRS system they use. They also don't provide any memorization/recall aids--they just present you with a word, and it's up to you to come up with a way to remember it.
iKnow also doesn't not teach kanji per se. Instead, they teach you words that happen to contain kanji. There's nothing wrong with that approach, but when I used it (in conjunction with Wanikani, at the time), I struggled with recalling any of the kanji I hadn't learned previously.
Besides the vocabulary iKnow provides (it is the source of the Japanese Core 6k/10k lists floating around the Internet, I believe), the community can also create their own sets of lessons--someone has created a set for Genki, for instance.
One thing iKnow does that Wanikani/Houhou doesn't do is English to Japanese recall--important if you want to speak and write Japanese.
iKnow, similar to Anki, is a tool I could see myself using again to fill in any gaps from Houhou and Wanikani.
Japanese Pod 101, more so than anything else on this list, is something I'll almost definitely come back to a little later in the learning process.
Japanese Pod 101 is a paid podcast that teaches spoken Japanese (they also provide tools to learn vocabulary, but I don't think they're that useful, especially compared to all the other options out there.)
I initially tried Japanese Pod 101 when I first started learning Japanese, and didn't find it that great. It was interesting enough, but I was (and am) primarily interested in learning to read Japanese. Additionally, the beginner lessons are very basic and mostly in English, so the listening practice is not that extensive. In my experience, the beginner lessons are not worthwhile compared to just learning the same information from a textbook.
From what I understand (I haven't personally verified this, however,) the intermediate and later lessons are much better for listening/speaking practice. Once I'm at the point I feel like my Japanese foundation is truly solid, and I want to improve my listening skills, I'll be re-subscribing and taking advantage of the intermediate (and advanced) lessons.