Electronic Text Corpus of Sumerian Literature (ETCSL) from Oxford University
https://etcsl.orinst.ox.ac.uk/ All the major texts are here but their translations are problematic because they are not translated to the scholars standard.
French School at Athens
https://cefael.efa.gr/site.php A depositary of reports from French archaeological excavations from around the Mediterranean. This includes the excavations at the Minoan city of Malia where many Linear A texts were discovered.
Internet Sacred Text Archive
https://www.sacred-texts.com/index.htm All the classics from all the spiritual movements up to the early 20th century. While the more ancient ones have problematic translations from the original, these texts reflect the spirit of the time in which they were written and are thus historical in their own right.
CELT
https://celt.ucc.ie/index.html CELT, the Corpus of Electronic Texts, is Ireland's longest running Humanities Computing project. It brings the wealth of Irish literary and historical culture to you on the Internet, for the use and benefit of everyone worldwide. It has a searchable online textbase consisting of over 19 million words, in 1638 contemporary and historical documents from many areas, including literature, medicine, and the other arts.
Project Gutenberg
https://www.gutenberg.org/ Great resource for books on which copyrights have expired. This includes a lot of translations of the classic Greek and Roman texts.
Perseus Digital Library
https://www.perseus.tufts.edu/hopper/ A Tufts University collection which has been under development since 1987,. It covers the history, literature and culture of the Greco-Roman world.
Internet Archive
https://archive.org/ Internet Archive is a non-profit library of millions of free books, movies, software, music, websites, and more. This includes the Wayback Machine which store old websites dating back to the mid 1990's.
https://lexlep.univie.ac.at/wiki/Main_Page Lexicon Leponticum is a digital edition of Cisalpine Celtic inscriptions and an etymological dictionary of the language remains documented in them. The site hosts a multimedia lexicon of Lepontic and Cisalpine Gaulish, the two Celtic languages spoken in the first millennium BC in northern Italy and in southern Switzerland. It also includes an edition of all objects bearing Lepontic and Cisalpine Gaulish inscriptions, and an etymological dictionary of the attested words.