A friend helped me acquire this particular book recently. Started as fan fiction online in Russia, then first published in book form in 1995, it has long been extremely popular in Russia. This new edition came out in 2022 and is already (I believe) sold out again.

At a very high level, it started as a reaction to The Silmarillion - a very one-sided history of Middle-earth. What if Melkor told his side of the story too?

More information is available at:
Чёрная книга Арды (Russian wikipedia entry)