Google Scholar - a search engine for scholarly literature, including articles, theses, books, and conference papers.
PubMed - a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics.
Web of Science - a citation index that allows you to search for articles, conference proceedings, and books across various scientific disciplines.
Grammarly - an online grammar checker that helps pinpoint grammatical errors, spelling mistakes, and punctuation inaccuracies.