BabelNet - Multilingual resource that covers hundreds of languages and, according to need, can be used as either an encyclopedic dictionary, or a semantic network, or a huge knowledge base.
LibreLingo - Experiment to create a community driven language-learning platform.
Toucan - Teaches you new skills while you browse the web.
Notation and thought - Collection of quotes on notation design & how it affects thought.
European Language Grid - European Languages Datasets.