The ARTFL project is a collaboration between France and the University of Chicago to digitally house a variety of French literary and language resources.
The project is basically a giant database. Although the main databases require a subscription, if you click “public databases” on the side tab a pretty substantive list of databases show up. If you are just researching general topics, or do not know specifically what you are searching for yet, I would recommend sticking with broader databases like JSTOR or ProjectMuse. If, on the other hand, you are searching for works from a specific author, or from a specific time period in French history, the ARTFL public databases can be of great use to you. One of the databases holds the works of Victor Hugo, another one houses a critical version of La Comédie Humaine. Each of the databases are different and require individual familiarization, but a lot of them have neat features. The database housing Diderot’s encyclopedia, for example, includes a tab on how to cite the encyclopedia in papers.
The other feature of this site that I would like to point out is its access to old language dictionaries. These are all freely available to the public, and you can find them by clicking on the tab for “Dictionnaires d’autrefois”. The great thing about this feature is that it searches three dictionaries at once for you. For example, searching “thresor” brings up two entries, one from “Jean Nicot: Le Thresor de la langue francoyse (1606)”, and another from “Dictionnaire de l’Académie française, 1st Edition (1694)”. As with most of the databases on this site, these dictionaries are very interesting, but not ideal for broad searches. They are great, of course, if you are specifically searching rare terms or old French terms.