LingBuzz is an openly accessible repository of scholarly papers, discussions and other documents for linguistics. Scholars are highly encouraged to upload their articles - old and new, published or not. It is run and hosted by Michal Starke They unfortunately categorize the submitted papers by phonology, semantics, syntax, morphology, and/or diachrony, so it is a limited resource for the rest of the field linguistics, but for what it hosts, it is the best.
Corpus Linguistics
CWPWeb at Lancaster hosts a very large catalog of corpora. It uses CQPWeb (Corpus Query Processor Web) and is currently hosted and maintained by Andrew Hardie.
TSCorpus is a free and independent project by Taner Sezer, a scholar in Mersin University, that also uses CQPWeb and is dedicated to building Turkish language corpora, developing NLP tools, and compiling linguistic datasets. TSCorpus is currently the biggest corpora hub for Turkish data.
Phonetics and Phonology
Interactive IPA Chart is one of the most useful tools I've used when doing phonetics and phonology homeworks. If you haven't built an intuitive sense of phonological distinctions yet this tool will save your life in phonetics and phonology.
Social Media Studies
4CAT is a research tool that is used for capturing and analysing social media data with ease. It currently supports collection from 4chan, Bluesky, Telegram, and Tumblr. For a larger catalog of platforms, check out the next tool.
Zeeschuimer works by saving what you see in the platform to it's history and creating a dataset out of that. You can upload Zeeschuimer datasets to 4CAT for detailed analysis.
Sign Language Linguistics
Spread The Sign is an online multilingual dictionary of sign languages. Useful for comparing signs from different sign languages or looking up signs quickly.
Syntax and Semantics
Miles Shang's Syntax Tree Generator If you are doing a syntax homework and you don't want to learn LaTeX overnight but don't want to upload a photo of your hand-drawn syntax trees either, this web application is a life saver. It's notation is so easy that even a sociolinguist like me could figure it out.
Miscellaneous
LinguisTree is an online and interactive academic genealogy website for seeing who was who's teacher. This is helpful to understand certain schools or traditions of linguistics. LinguisTree is a subproject of The Academic Family Tree where there is many more disciplines of science and their genealogies.