I just finished reading JK Rowling's Beadle the Bard (translated we're told by Hermione Granger) It consists of five tales with commentary by Albus Dumbledore that gives little tidbits about wizarding society.
The tales themselves are winsome and fun, but I found the commentary the prize. Lots of tidbits that could provide grist for the fanfic mill. No mention of Snape (or of Granger other than as translator.) But some Malfoy lore...
Such as that Muggle-borns are believed to have some magical ancestry in their family tree, listing some of the prior (mostly Dark Lords) owners of the Elder Wand (no witch has ever claimed to own it) that warlocks are specialists in dueling and martial magic, that anti-Muggle/Muggle-born/Blood Traitor slurs include mudwallower, bunglicker, scumsucker; a cold wizard who cannot love is said to have a "hairy heart"; and that Brutus Malfoy edited a "anti-Muggle periodical" Warlock at War in 1675 and that animosity between Lucius and Dumbledore sprang from his resistance to banning a book Lucius disapproved of. From the letter by Lucius urging the ban:
Any work of fiction or non-fiction that depicts interbreeding between wizards and Muggles should be banned from the bookshelves of Hogwarts. I do not wish my son to be influenced into sullying the purity of his bloodline by reading stories that promote wizard-Muggle marriage.