LEXIPEDIA is a great service for playing with words. It searches in the selected language and for a given word: meanings, synonyms, antonyms, loosely semantically related words, various parts of speech. This service shows the wordnet. When we click on the words and colored points, we will see definitions and examples of use. It's useful, for example when we write an essay.
If you are an app freak, it's good to use different applications to learning English too. I will show you many handy apps to keep learning English in a few minutes. Furthermore, I will show you many online dictionaries and websites to learn languages.