They’re unusual in word-processor layouts, but I don’t object to
columns: [number of columns]
Usually columns look neatest when the rows of text are aligned vertically between columns (i.e., as if they were sitting on the same baseline). Look at a decent newspaper for an example. Getting this result takes a little extra effort. Note your line spacing and make sure any space between paragraphs works out to a whole multiple of the line spacing. The two most common options: set space between paragraphs to zero, or set it to be the same as the line spacing.
On the web, though most of today’s web browsers support CSS-based columns, as a design tool they’re not that useful. Practically speaking, columns need to fit inside a fixed vertical space. But by its nature, a web page has an indefinite bottom edge. Still, columns can be useful in situations where you have a small amount of text or a list of links that can fit on a browser single screen. See system fonts for an example of this technique.