A dot plot shows one or more quantitative values per category by plotting one or more dots per category on a numerical (or date-time) axis. A dot plot with only one value per category makes a comparison between those categories very easy. When the dot plot has multiple values per category, you can also compare within the categories. This results in a chart type that packs a lot of information in a small space.
Since the dots communicate information via their position on the axis, and relatively via their position towards each other, the start- and end-point of the axis should be based on the minimum and maximum values in the data. There is no need to start the axis at zero.
By adding a connector between the dots, you can add an extra dimension to an already information-dense chart: The connector adds a focus on the delta between two values or the range between a minimum and maximum value.
The most simple alternative to a dot plot is a bar (or column) chart. Instead of using relative position on the numerical axis, the bar chart uses the length of the bar to communicate the value. To replace multi-series dot plots, one can choose between a stacked or a grouped bar chart. This makes comparison within and between categories possible.
A dot plot can be a pretty simple chart. Its minimum pack is categorical and numerical dimensions and a fixed size mark. Color is the thing that adds the edge to this chart. It might be used to place simple accents, but it can also add a new dimension: numerical, categorical, or even time.