PhilPapers is a comprehensive index and bibliography of philosophy maintained by the community of philosophers. The index currently contains 2,286,057 entries categorized in 5,268 categories.
The Stanford Encyclopedia of Philosophy (SEP) combines an online encyclopedia of philosophy with peer reviewed publication of original papers in philosophy, freely accessible to Internet users. It is maintained by Stanford University. Each entry is written and maintained by an expert in the field, including professors from many academic institutions worldwide.