Supplies a complete set of nice, round mesh-based water pipes, boxy item-transport tubes, and devices that work with them.
Adding simple storages for items, showing the item's inventory image in the front.
Extensive machinery mod with electricity and ores.
Produce biofuel from unused plants.
Adds components for building modular tunnel boring machines
Additional railway related content for use with Advanced Trains (advtrains).
Random digilines devices
The core of automation
Pipeworks, aka Tubeworks (see the last paragraph), is the best item transportation mod I've ever seen. While Minecraft-like hoppers could only transfer items down, Pipeworks could transfer items in different directions, or even sort them on-the-fly.
Many mods, like Technic, have support for Pipeworks, or even heavily depend on it, as Pipeworks provides an easily usable API for automation. You couldn't imagine how important Pipeworks is on the LinuxForks Minetest Server; most large factories and shops use Pipeworks to deliver items. Just be aware of the lag, which is the only disadvantage of installing Pipeworks on your own Minetest server.
An ironic fact is, as Rubenwardy mentioned, that the water pipe sucks, though the mod is named "Pipeworks". You should never download this mod if you are expecting a water transfer system, but you should definitely install this mod (the "Tubeworks" mod) if you want to move items around.
Nice mod for basic automation
Let tubes do heavy lifting, sorting and filtering. Nice automation mod especially when coupled with Technic
Tubeswork, but pipes don't
This mod is great for setting up factories to automatically process materials, I created a storage system using chests and sorter tubes.
Unfortunately, the liquid (pipes) part of the mod doesn't work that well, which is ironic
So this is essentially Minecraft's Buildcraft mod, minus the machines and power system. Which is fine, because having to convert between BC and IC power was a hassle anyway.
As useful as this mod is, it does have its shortcomings:
As for the good:
This mod isn't without its flaws, but you need to have it if you use technic (or just want to do any sort of automatic item transport.
Highly useful and widely used, however....
Autocrafters cannot accept item groups in their crafting grid, for example leaves, tree, wood, and many other groups which work naturally with crafting guides and user interfaces. (Listed on GitHub)
Injectors and tubes are not smart, and do not provide any versions that are smart which don't require extensive digilines detectors and Lua, which can know to stop pushing items if the next-in-line storage or tubeline are inoperable or full. It can even be lazy and deactivate the line on single spillage.
Injectors erroneously push items into the wrong containers, possibly skipping or losing instructions.
Tube routing is not intelligent, causing backups, spills, breakages, empty machines, and other problems. There should be automatic load-balancing with a toggle to select the old random switching or splitting/ round-robin.
Vacuum and other tube segments cannot properly interact with source liquids and flowing blocks, or falling blocks.
Large or complex constructs using pipeworks are known to have a major impact on server performance, and which some objects become out of sync or break when flooded. Abstracting the systems out of physical gamespace, and generalizing, network/ route mapping, scheduling, balancing, backgrounding, and offloading may have a positive impact on any server that runs this. Additional ways to allow servers the freedom to use pipeworks may include removing or reducing active objects and activities, reducing the thrashing of registered entities, simplifying and optimizing looping scripts, and scheduling all calculations while accurately tracking simulation speed and correcting for hiccups.
There are probably other common-use-case issues as well that are intuitively and reasonably desired which other players have discovered.
Must-have for every automated factory
Very useful for every automated system
Seriously, this mod is near perfect :)