Fallings sands can be played in your web browser on Kongregate. Note that the flash player on the site runs extremely slowly due to it emulating flash.
You can also play it through flashpoint which has archived the game. Download flashpoint and search for the game in the application.
Wikipedia has an entry about the type of game. In a falling sand style game, there is no objective, just an open sand-box for the player to play with. Typically the game gives you several types of particles that can be placed onto the field and the particles interact with each other in somewhat realistic ways.
For some reason I was fascinated with browser based games (usually made in Flash) at a young age. I made a couple of other smaller ones on Kongregate, but Falling Sands is by far the most popular. Unfortunately, Flash was shutdown in 2020 and by then, Flash games had already began to wane in popularity. Nowadays, browser based game are usually native javascript, but those of use who grew up in the early 2000s will always have a bit of nostalgia for flash games.
The original version of this game was originally coded in Java and was more geared towards being a physics simulator. Each particle actually had information associated with it such as specific heat, density, and viscosity. Movement was fully vector based. It was a cool concept, but ran extremely slowly. After some optimizations, I realized that this game had some potential, but it would never get discovered as a Java Applet on some obscure website. Therefore, I rewrote the game in ActionScript 3 for Adobe Flash Player.
Around 2010 I uploaded the game to Kongregate where it is still hosted today with around 2 million views. From 2010 to 2012 the game received a couple of updates such as new particles, but it is mostly unchanged since its original release.