Corpus de la littérature médiévale (Classiques Garnier). Purchased by Cornell in 2016. "The Corpus of Medieval Literature contains more than 800 French literary works, narratives, poems, and plays from the ninth through the sixteenth centuries. The database interface and texts in the Corpus are in French."
Société des anciens textes français: Scholarly society responsible for some 180 critical editions and facsimile editions. Some texts are available online through Gallica; this Wikipedia page provides direct links.
Classiques Garnier Numerique. Several corpus databases, purchased by Cornell in 2016. French, medieval to 19th century.
Gallica Digital Library of the Bibliothèqe national de France
1. Use the advanced search capability of New Catalog
type in box 1: texts sources (any of these; as subject)
type in box 2: french language (as a phrase; as subject)
add a box 3: century (example 12th) or date (examples: 1066 1500 1300) (any of these; as subject)
Many of the results will be anthologies or "readers" with excerpts of texts. Follow the footnotes and bibliography of these works for more complete or different editions of these texts.
2. LC subject heading: French Literature -- To 1500
Base de Français Médiéval (Ecole Normale Supérieure Lettres et Sciences humaines, Lyon)
Dictionnaire des femmes de l’Ancienne France (Dictionary of Women in Medieval and Early Modern France, 5th-18th c.; c/o SIEFAR – Société Internationale pour l’Étude des Femmes de l’Ancien Régime)
DEAF: Dictionnaire étymologique de l’ancien français (Universität Heidelberg)