If you would like to create your own mods, you can find a few modmakers on the Downloads page. Currently all these mods are for Diablo only, not for Hellfire, and they are for Windows only; there never have been any Macintosh mods.
Very unlike most others, this is a very friendly mod. There are no harmful shrines any more, those that give you a spell level don't take mana away any more. You need to click on Blood Fountains and Purifying Springs just once, and they will gradually restore your life/mana over time, as long as you remain on this level. You are healed as soon as you enter town. There are items that give you permanent infravision, there is a spell that outlines all items lying on the floor.
One of the goals was to add humor, and though occasionally silly, most of this humor is quite delightful. You will encounter Lag Monsters, Nasty Bitches and Newsgroup Trolls, and the zombies are called, in order of appearance, the Grateful Dead, the Ungrateful Dead, the Grateful Undead and the Ungrateful Undead. Beware the last, they still permanently take away some hitpoints.
This mod is rather extreme. The sorcerer is so weak at level one that he might be killed by a single exploding barrel. Bows have rather stiff strength requirements, and staves test dexterity as well.
This mod is supposed to change only uniques, both items and monsters. This is not entirely true. As soon as you start playing you will notice that the distribution of monsters has changed, too, a far wider variety is found on level one, including skeletons with bows.
Most everything else has indeed stayed the same, base items, prefixes, suffixes, spells, the location of Adria and Wirt. The biggest change you will notice is the vastly increased number of unique monsters, you will find up to four already on level one, if you aren't careful, you might be attacked by two at the same time.
Some of the new uniques are a bit absurd (like the Ancient Armor: 300 AC, but a durability of one), but most look really interesting.
The Sin War aimed nearly exclusively at the warrior, there are no unique bows or staves, so if you don't like to play a warrior, this mod might not be for you. If, on the other hand, the warrior happens to be your favorite class, it might be just what you've been looking for.
Their mod started it all.
You cannot download this mod any more from the homepage, but you will still find the documentation there. This mod is only available as a dat file.