I started working on this out of a serious need. I went about collecting various dictionaries in the wild and then aggregating data.
https://niai.mrahhal.net
Niai is a web app with 3 main features:
Type any amount of kanjis you want to lookup, the result will come back with a list of similar kanjis per each kanji. An example with 「枝方寄」:
The inspiration for this is @acm2010’s script
Those are words with same readings but possibly different meanings. An example with 「かえる」:
Simple enough, those are words sharing similar meanings. An example with “affection”:
This started as an experiment here: A tool to show useful aggregated data based on your WK level (homonyms, frequency, part of speech, ...)
A dark theme is also available!
Switch the theme from the button in the bottom left corner.
Kanji cards contain links to the WK level it’s introduced at, as well as a quick link to Jisho. Kanji and Vocab cards also display (and are ordered by) the frequency of the character or term (this is obtained from Innocent Corpus).
I also publish a swagger document for the api: https://niai-api.mrahhal.net/swagger
You’re free to use it however you like. Right now there’s no versioning but I’ll try to keep it backward compatible.
The whole thing is open sourced on github: GitHub - mrahhal/niai: Lookup similar Kanjis, Homonyms, Synonyms!. Any suggestions/contributions are very welcome!
Awesome stuff! I think you forgot to add the link to the actual site, though. 
http://niai.mrahhal.net/similar
Thanks for the site, I’m bookmarking it as I always confuse something 
Great work and thanks for sharing! I needed this for my Kanji journey and it’s always fun to check similarities and homonyms and what not
This is really impressive, did you enter the data yourself? If so then wow that must’ve taken a lot of your time
Thanks but I definitely didn’t heh. That would take me many lifetimes. I used several dictionaries and then aggregated the data into several feature categories. (The tool that does that is open sourced in the repo)
Looks awesome, but seems like the website is down. Is it down for good?
I’m having trouble keeping up with payments. There is a very unique situation in my country regarding international payments, and it’s getting worse each day. I have a limit (~$50) a month, and this month I wasn’t able to pay for the servers so I had to stop them a couple days ago. And paypal doesn’t work here either, so I can’t even accept donations.
So no not down for good. Only until I figure something out, or maybe next month if I’m able to pay 
This is a nightmare for someone like me, but there’s nothing I can do.
I’m really sorry to hear that! I hope things turn around quickly.
In the meantime, this is such a great resource, I’m sure the Wanikani community would step up to help keep it available. If there’s a way that it could be brought back on line sooner rather than later, it doesn’t hurt to ask or suggest!
Take care.
Thanks! Will think about what to do and post updates here.
@CrazyGundam and everyone interested. Want to let you know that because of some generous people donating, Niai is back online for the next few days. I was also finally able to get a friend to help me with setting up a PayPal account for anyone willing to donate to keep the server running, donation button is on the website.
Thanks