Landmarks is a worldgen mod that adds some natural features to the Overworld.
Other than aesthetics, the purpose of this mod is to make each area more distinctive through small-scale details that complement the existing large-scale terrain and biomes variations, and make it easier to recognize a certain place from looking around rather than using coordinates, hence the name. For this reason, the features are all procedurally generated and are neither ubiquitous nor rare.

This mod is server-side.

You can now add, modify and remove palettes with datapacks.

Rock Formations

Rock formations are highly diverse features that generate in every overworld biome (with some biome-specific variants). They can be made of different materials and can be small, big, isolated, clustered, smooth, rugged, etc.

Ponds

The loathed ponds are back from the grave. But they're not as frequent as in <1.17, and the partially buried kind is even rarer. They're also a lot more varied in appearance:

Forest Clearings

Areas without trees that break the monotony within forests:

Fairy Rings

Circular mushroom patches that generate within forests:

Thermal vents

They generate at the bottom of all deep oceans.

Sinkholes

They can have stagnant water.

More will be added...

Configuration

The mod is configured through datapacks that replace the integrated JSON files. Some of those are:

landmarks/tags/worldgen/biome/has_...
Control the biomes in which the features are generated.

landmarks/worldgen/placed_feature/rocks.json (Continental rocks)
landmarks/worldgen/placed_feature/ocean_rocks_deep.json (Rocks that emerge from deep oceans)
landmarks/worldgen/placed_feature/ocean_rocks_shallow.json (Rocks that emerge from shallow oceans)
landmarks/worldgen/placed_feature/underwater_rocks.json (Submerged rocks)
landmarks/worldgen/placed_feature/forest_clearing.json (Forest clearings)
landmarks/worldgen/placed_feature/pond.json (Ponds, oases, frozen lakes)
landmarks/worldgen/placed_feature/fairy_ring.json (Mushroom rings)
Can be used to tweak the rarity of the features, or disable them altogether.

landmarks/worldgen/configured_feature/rocks.json
landmarks/worldgen/configured_feature/pond.json
landmarks/worldgen/configured_feature/forest_clearing.json
landmarks/worldgen/configured_feature/fairy_ring.json

Also check the wiki.

Note that although this mod appears to reuse Minecraft's density function system, in practice most vanilla function types (noise, cache and interpolation ones in particular) and everything that depends on them (such as overworld biome parameters) don't work on Landmarks features, and Landmarks analogues don't work outside of its feature type.

Future plans/ideas

Improve the aesthetics of the rocks and clearings, I'm not yet satisfied with them
Add more types of ponds
Ocean isles, volcanic islands, atolls?
Floating islands above deep oceans? Not sure if they fit into the theme of the mod, but they would make oceans more interesting
Moss patches and tree stumps in forests
Mud volcanoes?
Animal trails?
Tidal pools?
Animal nests?
Mini caves?
Make use of the new 1.21.8+ blocks
Improve the documentation of the config format