The following resources present extensive collections of Ancient Greek texts online. Some are open-access, but others are subscription-based and require a login. The resources designated as "Core Collections" are absolutely indispensable to all scholarship engaging with Ancient Greek in the original language. "Other Major Collections" include corpora with more specific areas of focus.
Login required: The digital Loeb Classical Library presents an interconnected, fully searchable, perpetually growing, virtual library of all that is important in Greek and Latin literature. More than 520 volumes of Latin, Greek, and English texts are available in a modern and elegant interface, allowing readers to browse, search, bookmark, annotate, and share content with ease.
Tesserae is a freely available tool for detecting allusions in Latin and Greek texts, both poetry and prose. The database encompasses over 100 Latin and over 70 Greek authors, allowing a researcher to compare individual texts or different authors' corpora. For an overview, see here.
Personal login required: Founded in 1972, the TLG represents the first effort in the humanities to produce a large digital corpus of literary texts. Since its inception, the project has collected and digitized most texts written in Greek from Homer to the fall of Byzantium in AD 1453.
Open-access: Produced by the German Bible Society, Academic Bible is the leading website for academic biblical studies. It provides free access to the Rahlfs-Hanhart edition of the Septuagint and the UBS edition of the Greek New Testament.
Open-access: The Bibliotheca Augustana is a digital collection of texts compiled by Professor Ulrich Harsch since 1996. The Greek texts are based on several different editions, including older ones from Teubner. Note, however, that Harsch does not include the critical apparatus with the texts.
Login required: Brill's New Jacoby is a fully-revised and enlarged edition of Jacoby’s Die Fragmente der Griechischen Historiker, providing new texts of the ancient historians in many instances as well as several new historians and many new fragments of existing historians that were either unknown to Jacoby or excluded by him. It also offers facing English translations; new, critical commentaries; and a brief entry about each historian’s life and works, with a select bibliography.
Open-access: The Corpus Medicorum Graecorum (CMG) presents the extant writings of all Greek physicians from the 5th century BC to the end of classical antiquity, including Galen's works (by far the largest collection of extant writings by a single Greek author), and early Byzantine handbooks and commentaries on ancient authors, in historical-critical editions. The Supplementum to the CMG publishes collections of Greek medical writings which have survived only in fragmentary form.
Open-access: Part of the Open Greek & Latin initiative, the goal of this project is to collect at least one edition of every Greek work composed between Homer and 250 CE with a focus on texts that do not already exist in the Perseus Digital Library. All the works in the repository with added metadata are listed by author, and include links to the individual files.
Open-access: Still in development, this resource stems from an international partnership between Harvard and the Center for Hellenic Studies, the University of Virginia, Perseus, the University of Leipzig, and other institutions. Open Greek & Latin features a corpus of digital texts, deep-reading tools, and open-source software. All materials can be downloaded, modified, and redistributed in accordance with all applicable licenses.
Open-access: An edited collection of writings by the early Church Fathers and ecclesiastical authors writing in Greek from the beginning of the Christian era until the fifteenth century. It consists of 161 volumes published in 1857–1866 by J. P. Migne. This source links to Google Book versions of each volume, and is accompanied by Latin translations.
Open-access: Produced by the Packard Humanities Institute, this tool is a comprehensive database of all ancient Greek inscriptions. For an overview, see here.