glottolog.org
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Glottolog is a comprehensive, language-centered catalog of the world’s languages and dialects with unique Glottocodes and a historical–comparative classification. It provides extensive bibliographic references and links to descriptive sources (grammars, dictionaries, wordlists) for each language.
More resources on Historical & Comparative
The Horse, the Wheel, and Language
An archaeologist's case for locating the Proto-Indo-European homeland on the Pontic-Caspian steppe, combining linguistic reconstruction with excavation evidence on horse domestication and wheeled vehicles to explain how the language family spread across Eurasia.
Miracles of Human Language
Leiden University's Coursera course, taught by Marc van Oostendorp, surveys how human languages differ and what they share, with interviews of native speakers and guest linguists. Completing it gives a working grasp of phonology, morphology, syntax and language typology.
etymonline.com
Online Etymology Dictionary is a comprehensive, searchable resource that traces the origins and historical development of English words, detailing word roots across languages (Old English, Latin, Greek, etc.) with concise etymologies.
Historical Linguistics
Historical Linguistics - A book resource
indo-european.info
Indo-European.info is a scholarly resource for historical and comparative linguistics focused on the Indo-European language family. It provides overviews of language branches, Proto-Indo-European reconstructions, phonology and grammar notes, etymologies, and links to related resources and datasets.