Plumbing-oriented:
Classically, for threaded pipes, you use a union, or two unions.
Modernly, it's trivial with push-to-connect fittings.
It's also classically trivial with soldered connections. Sometimes brazed rather than soldered, depending on the "industrial" nature of the process.
(for the example shown in the link, given no need to hold water, probably the side connection pipes are loose in the threads from having been partially unscrewed to make the connection; or else the threads have been drilled out on one side.)
For considerable investment in tooling, you could use left-handed and right handed threads on opposite ends of a pipe nipple so that it can be screwed into both ends at the same time to make tight connections. For a manufacturer who's found a market for things like you show in the linked picture, that could pan out; for a DIY project the costs would not make much sense.