Although the user interface seems quite outdated, YellowBridge is a quality, comprehensive dictionary and thesaurus for Chinese characters. The website breaks down each character, providing related words, synonyms, antonyms, example sentences, interactive stroke order diagrams, etymology, and more. Subscribing to the site gives you access to more features, such as derived words or similar-sounding words.
They also have pre-loaded flashcards and memory games for several common textbooks, such as the New Practical Chinese Reader or Integrated Chinese. However, these flashcards don’t seem as intuitive as Pleco’s system, so it might be more effective to download a user-made deck for your current textbook and input it into Pleco.
YellowBridge keeps up to date with current issues and helps you learn the vocabulary of today — on the side, you will see a section of “words in the news,” which lists popular phrases that are circulating around the world.
Beyond the language learning tools, YellowBridge also has some cultural notes on humor, literature, mysticism and divination, and famous Chinese Americans. These are probably not the site’s major selling points, but they may be a fun read.