Dangers & Dweomers is a retroclone of Dungeons and Dragons, partway between the original D&D rules and the Advanced Dungeons & Dragons rules, to produce what it calls an "Advanced Basic" version of D&D.
Here are some of the difference compared with basic D&D:
Assign 4d6k3 to ability scores of choice (rather than 3d6 in order)
Race is separated from class (races include class restrictions, certain special abilities, and ability score modifiers)
Classes have some additional special abilities
Dual-class characters are allowed
Nine alignments, [LNC]/[GNE] (rather than just three, [LNC])
No alignment languages
Secondary skills included (these were optional rules introduced in later D&D supplements, but became core by the Rules Cyclopedia)
Base Armor Class of 10, with higher values being better (as opposed to a base of 9 with lower numbers being better)
Experience Points for treasure are at a rate of 1XP per silver (rather than 1XP per gold)
Aside from monsters and treasure, XP are also available through individual achievements and class-related awards
Turn Undead table is subtly different (it is listed by Hit Dice rather than specific type, and includes "Demon" rather than "Special" as the highest entry)
There are schools of arcane magic and clerical domains (which didn't exist in Basic D&D)
The spell lists are similar, but not exactly the same comparing Dangers and Dweomers and Basic D&D (it's much more like the AD&D spell lists)
Monsters have Challenge Levels (in addition to the rest of their characteristics)
Monsters include some non-D&D creatures (such as all "Outsiders", a term which didn't appear in Basic D&D)
Some additional optional campaign rules are included, some of which were not in Basic D&D
Treasure is related to Challenge Level (rather than by treasure types)