shouldering each other's dreams...

anki

Anki
flashcard app for windows, mac, linux, android, and ios. highly customizable, with access to a ton of different user made plug-ins and decks. i recommend using the FSRS algorithm for scheduling your cards instead of the default SM-2 scheduler, which you can learn about here.
FSRS4Anki Helper
add-on to help customize your card schedule if you use the FSRS algorithm.
ReColor
lets you customize the color palette of anki.
Pass/Fail
removes the easy and hard buttons, so you only have to decide between passing or failing a card.
Opening the same window multiple time
lets you open multiple instances of the same window type (browse, add, edit, etc). personally i add "AddCards": false, to this add-on's default configuration so i don't open dozens of add card windows when i'm sentence mining.
Generate Batch Audio
automatically pull audio from sources like forvo and add them to the selected cards.
Yomichan Forvo Server
adds forvo as a source for word audio in yomichan. compatible with yomichan forks like yomitan.
VOICEVOX Japanese Text To Speech Audio Generator
uses VOICEVOX speech synthesis software to generate audio for your anki cards. i'm generally against using TTS software too much when learning a language but VOICEVOX is pretty high quality for a free TTS so i'll use this when i really want a reading of a given sentence. only works with japanese.

browser tools and extensions

Yomitan
interactive pop-up dictionary. built for japanese but support for other languages is being worked on. some non-japanese dictionaries that work with yomitan can be found here.
Language Reactor
chrome extension that allows you to view 2 subtitles simultaneously on sites like youtube and netflix as well as their own video viewer. has a built in pop up dictionary. you can track known and unknown words if you pay for a pro membership.
asbplayer
media player and chrome extension that allows you to easily create anki cards with sentence audio and screenshots. the subtitles in the media player are also text selectable so you can use them with pop up dictionaries like yomitan.
Filmot
tool that lets you search a word or phrase within the captions and subtitles of over 800 million youtube videos.

applications

Mokuro
tool that processes manga, creating html files with selectable text so you can easily look words up and create anki flashcards using a browser-based popup dictionary like yomitan. you can find a collection of preprocessed manga here.
jidoujisho
android app with built in video player and ebook reader that lets you easily look up words and export flashcards to ankidroid. can read/watch local files and online sources like youtube. supports mokuro processed manga as well.
GoldenDict
a powerful dictionary app. supports a number of dictionary formats, audio, and automatic scanning in any application. there is a fork, GoldenDict-ng, that adds anki integration, but on my machine i find the original GoldenDict to be more stable. in addition to GoldenDict-ng's documentation, i recommend checking out tatsumoto's guide on setting it up. you can find a ton of dictionaries and audio repositories for many languages here.
@Repth