The MCDF Wiki is a wiki that documents discontinued features of Minecraft, the wiki has sections for Java Edition, Bedrock Edition and Console Edition.

The Minecraft Wiki is a wiki that documents general information about Minecraft, it should be noted that the Minecraft Wiki has recently moved off fandom to minecraft.wiki

Burger Web Viewer is a website that can show the differences between two versions, it extracts practically any and all data from the the two version's jars and gives a readable comparison between the two versions.

MC Property Encyclopedia is a website that lets you search or query many different block properties, this can be very helpful for finding the right block for a redstone build or technical setup.

wiki.vg is a wiki that documents internal protocols, formats and other data with in minecraft. This wiki is a good place to find information when building a tool for minecraft that needs to work with internal data.