Conveyor Splitter

A Conveyor Splitter is a building that takes items from a single input Belt and outputs them between three other belts. If an output belt is not fast enough and gets stuffed, and if any filter applied allows it, the items on the input belt will be divided equally between all others non stuffed output belts. If all output belts are blocked, the items at the input belt will have to wait.

Types
There are three types of splitters available, each with different sorting capabilities.

Basic
The standard splitter appears to simply split items between its outputs in sequence. If any output is full, it will distribute the incoming items into the remaining outputs evenly.

Smart
Splitter with 3 outputs. Each output can have a filter set to either "none", "any" or one specific item type.

Programmable
Splitter with 3 outputs. Each output can have multiple filters.

Building
The and  have fairly large collision boxes which are likely to obstruct additional parallel belts. For example, a splitter for belt is likely to block the construction of  belt. It is advised to build other nearby belts before building the splitter/merger.

Trivia

 * It is easy to differentiate between input slot and output slot by looking at the shape of LED light at the belt connector. The output is indicated by a arrow-like light, while the input is 3 smaller dotted light.
 * Splitters will only split across the number of outputs you use. So you can divide the input into two halves, or three thirds.  This is a useful characteristic to apply in efficient early game set-ups for e.g. smelting ores, which are predominantly simple ratios of 1 to 2, 1 to 4 or 1 to 8.
 * Planning ahead, get into a habit of adding a Conveyor Splitter before every input of production buildings. This allows you to expand a line of production buildings later on.