The Liquid Webtoy is an interesting fluid simulation made by DAN-BALL. It is similar to the falling sand games, but it uses round particles instead of one-pixel particles, as well as having more liquids. You can change the background, if the elements have outlines, etc. There are many different elements:

Water: Basic element. Sloshes around.

Paint: Changes the color of water. You need Hit turned on to use this.

Cloud: A cloud, which when it hits the ceiling, turns into water. Also carries ducks.

Magma: Makes ducks red, and turns water into cloud.

Ice: Makes ducks blue, and freezes water.

Wall: Blocks other elements, and serves as a platform.

Bomb: Pushes other elements away.

TBomb: A timed bomb.

Duck: Your poor test subjects. Please, think of the ducks!

Clear: Erases wall.

Black Hole: Pulls in all elements except wall.

 Summary

Garry’s Mod is a mod for  Half-Life 2 made by Garry Newman. In Garry’s Mod, you can spawn objects/props from the game and make contraptions, pose the characters from the game, make the characters fight you or each other, and more! There are various tools to make contraptions: Here.

 Modes

In Garry’s Mod you can play online (or LAN) Multiplayer, or Singleplayer with yourself. Each of these modes have different advantages and disadvantages.

Multiplayer lets you build or fight with other players, as well as make minigames (like racing cars you made). Also, many maps are made just for multiplayer, such as SpaceBuild, where you team up with other players to colonize planets and explore space. However, in Multiplayer you can not save your contraptions (unless the server has Advanced Duplicator… but then you can only use the contraption on that server), as well as having to deal with spammers and “MingeBags” (the Garry’s Mod term for players that mess up other peoples’ creations). Some servers try to stop that by having spam protection and prop protection, but “MingeBags” can still get around it by using duplicator or dynamite.

In Singleplayer you can build contraptions without worrying about spammers and “MingeBags”. You can also save the contraptions you have made. You can fight the AI characters without making a Server Admin mad, too.

Videos

World of Sand

The first falling sand game. Wall can be used as a platform for particles. Water floats on sand and helps plant grow. Fire burns oil, plant and cera. Plant grows with water, blocks ???, and acts like a burn-able wall. Sand eats spout, and salt eats namekuji (the rolling thing). You can turn namekuji off, stop it, or just let it run around.

Hell of Sand

World of sand, with some small modifications… including… ZOMBIES!!!

FallingSandGame.com

A fan site for the falling sand games. The members made many new versions, both online and downloadable. Here are some notable modifications:

Pyro Sand

More explosive elements than the original, as well as concrete, well (makes oil) and torch (makes fire). There is also a second version which has a few more elements and a better menu.

WxSand

A downloadable version. It has more elements, as well as the ability to be modded. It also has more options, such as a gravity toggle.

Burning Sand

Everything WxSand has, but instead of text for the elements there are pictures.

Sand 3d

The falling sand games in 3d. A bit hard to make straight walls, but that will probably be fixed soon.