Free, Open-Source Software (FOSS) is one of my passions in general, but there are some great pieces of FOSS software which can be used to learn Chinese (or pretty much any other languages). There are programs to help you with vocabulary and flashcards, as well as free dictionaries which are useful even as a professional translator. All of these programs contributed heavily to my ability to learn Chinese. This is by no means an exhaustive list, this is just the stuff I have found the most useful learning Chinese and even working as a translator.
Anki
Anki is a flashcard program with a lot of features. Anki isn’t just good for language flashcards, it’s great for memorizing pretty much any kind of flashcard. It supports images, sounds, video, etc. embedded in cards as well as multiple different values per side. Anki also has a huge number of free decks available and which cover all sorts of topics.
If you are working from a given textbook, you can typically just search the textbook’s name and “Anki deck” and find a great deck to build off of. The HSK has some amazing decks if you search for them. There are decks like Timo’s All-In-One Deck and other decks for just HSK vocabulary. Anki is also great for other languages and subjects as well.
StarDict
StarDict is an amazing dictionary program that I used when I professionally translated. The format itself is lightweight and there are hundreds of dictionaries you can find. Dictionaries can range from basic learner dictionaries to comprehensive Chinese-Chinese dictionaries to extremely obscure technical dictionaries. You can find pretty much any language to any language if you know where to look.
StarDict allows you to have scanning on word selection, have dozens of dictionaries to where you barely notice they’re searching, and allows you to enable and disable various dictionaries as necessary without removing them. I find it extremely useful for translation and general study both. StarDict’s interface hasn’t really aged the most gracefully, but in terms of function and raw speed, it is second to none.
GoldenDict
I personally prefer StarDict on most systems, but there is also GoldenDict which adds a bunch of features and has a much better GUI on Windows and Mac. I use GoldenDict on either of these platforms as it tends to be a bit more stable on Windows or Mac than StarDict (without tweaking at least). Resource-wise, it isn’t too much heavier once it’s set up and going, but I find it a bit slower than StarDict even on better hardware, though not by enough to be a deal breaker.
GoldenDict beats StarDict in format support as it supports many other types of dictionaries which StarDict does not. There are tools to convert them in most cases, but it is a lot easier to just drag and drop some dictionaries rather than learning a bunch of tools to convert something once. Some formats do not always convert the best with certain options, so it’s much easier to use something that opens basically everything common. GoldenDict also has the option to use web dictionaries which are much easier to work with.
CEDict
CEDict is a Creative Commons licensed Chinese to English dictionary. It contains the simplified and traditional (where relevant) characters, as well as Pinyin and the definition. CEDict uses a common format, but is easily available in almost any format of dictionary software you can think of. The quality of translations and the quality of the dictionary overall is extremely good (consistency of characters, correctness of Pinyin, etc.).
ZDT
ZDT is an open-source Mandarin flashcard application in Java. This is a pretty good all-in-one program combining some of the strengths of all of the above into a single application. It isn’t really the best at any of the tasks, but it was extremely useful for me when I first started learning. Its primary strength is that it is okay at everything, but easy to get a lot of information from a single source. You won’t feel it excels at any task too much, but it was a single application to make my beginning, textbook-based Chinese learning much simpler.
Rime
Rime is an open source, cross-platform Chinese IME. It supports both simplified and traditional input and is one of the few open source IMEs available on something other than Linux or BSD. I admit I’ve only worked with it sparingly as I tend to use IBus primarily on all of my Linux machines.
Rime is one of a kind because of its platform flexibility and the fact that it supports so many different input methods basically out of the box. The site is in traditional characters when you first arrive, but there’s a button to automatically convert. I did not see a button for English, so that may be a deal breaker or make the software functionally inaccessible for some people.
Mobile
Anki and GoldenDict both have mobile versions, though they do cost money on some platforms. The mobile versions are extremely high quality and work well. There are also plenty of FOSS Stardict equivalents (specifically, software which supports Stardict format dictionaries) in multiple free app stores as well as the Play Store for Android. Last I checked, there were near half a dozen or so I stumbled on, so I can’t really commit to a specific one. Rime also has an Android client if you have an Android phone and want it across the board.
Ubuntu Kylin
If you want to take the plunge on a Chinese language OS with minimal setup and for free, check out Ubuntu Kylin. Ubuntu is one of the easiest Linux distributions to work with and pretty much just works when you plug it in. Ubuntu was the first distribution that really got me hooked and showed me how easy the world of Linux was.
It’s FOSS has a great read about Ubuntu Kylin which will you give you a lot more information than a small blog post to say the least. Ubuntu Kylin boasts having a lot of extra software which is makes working with Chinese a lot easier than on some platforms. There are some common Chinese packages which are not open source available when downloading Ubuntu Kylin as well.
Conclusion
This is just a small sampling of what is available, but it encapsulates my favorites. Some of these programs easily replace commercial offerings like Stardict or Goldendict, while others are basically the only standardized option like Anki. You can even replace your entire OS with something FOSS to help you learn. The number of options are staggering and the quality is superb.
Even mobile platforms have an abundance of FOSS programs and apps which can be used to further your Chinese learning. Many of the previously mentioned programs have mobile clients in some form or another, or at least a similar option. I turned to FOSS for most things years ago and haven’t looked back. The quality of FOSS is outpacing many commercial options to the point of absurdity almost. Try it out and see what works for you. Tell me if you know of anything I missed or which helped you!