Courtesy of jdgleaver -
Introducing the concept of RGUI particle effects. Basically, you get 256 particles to play with, each consisting of 4 float variables with which you can do as you please. This is very crude and simplistic, but it's also quite flexible and adding new effects is a fairly trivial exercise.
From a user's perspective, the current Snow option has been removed and replaced with a new Background Animation setting under User Interface, Appearance. This can be disabled, or set to one of the following:
Snow (Light): This is the existing snow effect
Snow (Heavy): Same as above, but with variable (larger) snow flakes
These animations of course have a performance impact. They make RGUI update on every frame (just like ticker text), and they increase the performance overheads of rgui_render() anywhere from 38% to 59% on average. Much of this can be mitigated by disabling borders, however.