anki
Besides text, it supports sounds, images and rendering TeX snippets in the cards. It can synchronize card decks to a server so that you can review the deck on other computers, a web interface or mobile devices, for which versions of Anki are also available. Complete card decks offered by other users can be downloaded the same way.
Anki is extensible with plugins which can be downloaded and installed from the menu. While Anki can be used for studying anything, plugins are available with special features designed to make studying Japanese and English easier: integrated dictionary lookups, missing kanji reports, and more.
Latest reviews
I like it lots. Simple, direct, extra features for those that want, sync to web, easy to make cards, decks to share... i'm still a newbie but i'm liking it so far. Oh, to install on a fresh Linux Mint, i also had to "sudo apt-get install python3-distutils" in terminal.
Long-time Anki lover from other platforms. As mentioned by another reviewer, post-install the program does nothing until you run "sudo apt-get install python3-distutils". Then it works fine.
I had to run "sudo apt-get install python3-distutils" after installation to get it running, but anki still deserves five stars.
Great for learning vocabulary for new languages. It keeps track of all your words, so you don't forget to review any. Nice graphs to show your progress, too.
Helps learning anything (even on Android) and is highly configurable. It provides lots of shared decks, none of LinuxMint yet ;-)
But software version is out of date a long time ago. Now you even can't it, because right after install you are receiving message that update is required.
This package is out of date, you can get the latest version (2.0.8 +) from their website.