Kaguya-sama's Browser History
Launching the ancient artifact known as Internet Explorer 6, you are overcome with waves of nostalgia. In short order, your childhood memories fade away and the desire to know Kaguya-sama's most intermost secrets takes hold.
Clicking the browser's history button, you are greeted with a flurry of different websites! Apparently clearing your browser history isn't common-practice in Gensokyo.
Friends of the Site
Dzsekszon.net - A comfy collection of doujin music.
This website has a smattering of the owner's personal doujin favorites and rips, all sorted by event and playable right inside your web browser!
Exiting the music corner and having a stroll through the rest of the site can be a bit of a trip.
He has taken special care to ensure that the site is accessible without dirty javashit while still maintaining full functionality.
PS: It is pronounced "dʒæksən" and means the son of Jack.
PSS: He keeps bullying me to update this site :(
Herz.moe - Some crazy wunderwaffe run by an even crazier german. The site is agressively moe and heavily stylized. You can click on almost everything and it will do something! The owner is a fellow dot-fag and enjoys puzzles.
Small internet communities
danger/u/ - A real life clone of Va-11 Hall-A's danger/u/! This is a textboard modeled after a phone app in the cyberpunk waifu bartending simulator. /u/ and /v/ are the most active boards. Best viewed on phones due to the forced vertical layout, but with some simple css tweaks using a browser plugin like Stylus you can get it running in a more desktop friendly layout. The site has a problem with russian spam, so be careful of any links that get posted. Also the banners are sentient and burg posting will always remain in balance.
Kissu.moe - My personal favorite alt-board. It's overall theme is otaku internet interests, so most weeb topics are acceptable. I feel like it has an overall friendly and comfy tone without feeling forced like on Sushican. One of their stand out boards is /cry/, a Higurashi themed board were discussion of the series can be done without having to deal with adding spoiler tags to things. Overall the site has a fair amount of activity, but not to the point that you would miss anything by just browsing /all/ expect /cry/, thats not on /all/.
Lainchan - One of the more popular english imageboards that isn't 4chan. Characterized by most posts being technology or cyberpunk focused and the site's motif being based on Serial Experiments Lain. There is a certain level of doom posting there that when mixed with the Lain theme gives the site a very unique atmosphere. The site runs on a heavily customized imageboard software and they run their own irc and mumble servers. The community has also started it's own webring of sorts, again most of the sites are interesting and I hope to add them to this list eventually.
Lewd.sx - A social forum centered around the shared interest in cute anime girls, lewd things, and shitposting. Appears to have fallen from grace, but the remaining community is very strong and welcoming. The site recently underwent a redesign and gained a surge of users, but this hype was short lived. A refreshing change of pace if you are used to the downward spiral imageboards and reddit have been in the past several years.
MVGroup - A forum/torrent tracker for documentaries. An unholy god send when you are looking for that one documentary series that no one else has online. You are required to have an account, but registration is always open and you don't need to worry about seeding ratios or anything.
The Post Office - An easy going anonymous text board. It's slow, but most of the posts are of high quality. The site also has a public television of sorts where you can add youtube links that act as channels. There is even an image section where you can simply post an image for everyone to see, but not reply to.
Sushichan - The comfy imageboard, themed after the atmosphere of a sushi bar. Sushichan is currently under the management of Seisatsu, someone who has taken up ownership of other small sites that were about to shut down. The /otaku/ board is one of the homes for the refugees of the recently closed Samachan and it effectively the site's /a/. They have an IRC, but after observing it for about a month it is incredibly slow.
Uboachan - An imageboard dedicated to Yume Nikki and NEETs. Another imageboard that is under the ownership of Seisatsu. The NEET boards are of particular interest if you want some good posts to read. They have download links for the classic version of Yume Nikki in the sidebar.
Online Tools
Awesome Drinks - A database of cocktails with properly indexed ingredients. Though rather limited, you can plug in what you want/have on hand and it will spit out a list of cocktail recipes. Each drink has a small blurb for the taste and instructions on exactly how to mix it.
Global Consciousness Dot - The Dot requires no introduction. Tapping into the minds and computers of everyone in the world, The Dot knows all. Check the Dot. Interpret the Dot. Worship the Dot.
Jisho - A good Japanese-to-English dictionary. While it works great for finding out what different Japanese kanji means, it also provides furigana pronounciation guides. You can pair this with Whiteagle (covered below) to properly convert Japanese kanji and kana into romanji.
SauceNAO - An image search site that indexes sites like pixiv and danbooru. Incredible for finding the original quality images of anime fan art or lewds. It can also somewhat do visual novels and anime. Their browser plugin is really good and allows easy image searching from right clicking an image, even if you don't want saucenao searching capabilities.
Szynalski's Tone Generator - An easy to use tone generator. Perfect for testing audio equipment like how low your subwoofer goes (and where all those rattles are coming from), if your diy crossover works, or how deaf you are.
What Anime Is This / Trace.moe - In a similar vein to SauceNAO, but for anime. Just feed it a screenshot from an anime and it will do its best to find the original source!
Whiteagle - A very simple and easy to use kana to romanji converter. You can simply dump Japanese kana into the big box and it will spit out the romanji. It can also be used to convert hiragana to katakana and vise versa.
Japanese Media in English Databases
AniDB - A far more expansive catalog of anime compared to MAL or Anilist. They have loads of information on things like fansub releases, soundtracks, and have a thorough tagging system. The section on music releases related to each anime is especially helpful if you are trying to put together a complete collection. Also my favorite Plex metadata source for anime.
Kaomoji.ru - An extensive list of Japanese emojicons broken down into different catagories based on meaning or what they are. The site is techinically in russian by default, but it has an english translation! It includes a briefing on what kaomoji are and then each section breaks down how different characters are used in kaomoji. The list of emoticons isn't the most complete thing out there, but with the information provided you should be able to decode any you stumble upon or even make your own!
MangaUpdates - The manga division of Baka-Updates. By far the best source of information on manga. They catalog official releases as well as tracking fan scanslations. Baka-Updates itself is long dead, but their primary function can be replaced with AniDB.
THwiki - The ultimate Touhou music database! So this one isn't actually in English, but anyone who's prepared for the future knows chinese, right...? No? Well, you'll figure it out anyways. The site is easy enough to navigate with zero bug-speak knowledge. Just the sheer wealth of information and amount of cataloged Touhou doujin music on this site makes it worth using.
TouhouDB - One of the better English Touhou doujin music sites. An offshoot of the popular Vocaloid site VocaDB, it includes a slick UI, the ability to link to Youtube videos of songs, and built-in music player for said videos. They pull a lot of their information directly from THwiki and include refernce links to other sites. That being said, TouhouDB is still young and doesn't have as extensive coverage as the chink wiki. still better than VGMdb tho
VNDB - For visual novels, nothing beats The Visual Novel Database! They attempt to track every single release of every single visual novel, including fan patches. The tagging system is extremely thorough and makes finding specific VNs easy with their search engine.