The tabu package contains a lot of very nice ideas that are worth having. Unfortunately, however, it hasn't been actively maintained by its original author since 2011 and that means that a number of bugs have been discovered in the last years that are all unfixed.
This source code repository does not mean that members of the LaTeX Project Team are now actively maintaining this package.
The package is, and will stay unmaintained unless a new maintainer steps forward.
All the team tried to do with this repository is to provide some
emergency fixes (which was/is difficult enough) that were necessary
because tabu stopped working altogether after the latest corrections
made in the LaTeX kernel. However, as it turned out it is impossible
for us to fix all the problems with this package and we are unlikely to
try further.
Note that the GitHub organisation name has been changed to clarify the intent
it is now
https://github.com/tabu-issues-for-future-maintainer/tabu
Please update any links that still use the old name
https://github.com/tabu-fixed/tabu
although GitHub should redirect any existing links.
We welcome and appreciate bug reports through the issue tracker, because we hope that at some point in the future there will be a new active maintainer for this package. However, we aren't necessarily going to act on any issue, especially not on issues that are not caused by recent changes to the LaTeX kernel code (but even those have their reason in the past as the package patched a lot of LaTeX internals that should have never been done or only if there is an active maintainer lookin after them).
In summary: while this package is nice, there is no guarantee that it will not break again in fact it is still broken in some parts. If that happens it could be that no easy fix is possible. Due to the complexity of the code it takes time to determine the root cause in case of problems and often even more time to sucessfully mend the code---time that the team doesn't really have. It is therefore very important to consider carefully if you want to use that package in any important document (say, a thesis), because half way through you may find that it stops working (like tabu recently did) and there may not be a fix possible within your timeframe.
We therefore do not recommend its usage at this point in time. However, we hope that somebody will step forward and start actively supporting the code base.
--- The LaTeX3 Project Team
tabu provides a single environment: tabu designed to make all kind of tabulars provided that they do not split accross pages.
tabu is based on array.sty and requires no other package. tabu does not modify array.sty nor the classes of tokens.
Starting from version 1.5, longtabu is provided: based on longtable, longtabu allows tabulars to stretch out on several pages.
tabu can be used in place of tabular, tabular* and tabularx X columns in tabu can be specified with a width coefficient the alignement (l,r,c,j) the column type (p,m,b) or even $.
tabu also works in math mode and its name remains tabu.
tabu can contain any type of tabular, array, tabularx
tabu can be put inside tabular, array, tabularx, tabular*
\begin{tabu} is like tabular if the preamble has no X column
\begin{tabu} to specifies the target width
\begin{tabu} spread enlarge the natural width
tabu with X columns has a default target if not specified (usefull for nested tabus + compatibility with \linegoal)
tabu provides facilities to change the font and the alignment in one row (\rowfont), save and restore the preamble and the tabular parameters (\savetabu, \usetabu, \preamble).
tabu provides other facilities to align numbers in X columns draw lines with color, dashed or even leaders. Those facilities are provided for convenience: they work as long as the tabu preamble does not contain "too special tokens".
tabu has been tested successfully with many packages related to tabulars, cells, alignment...
The original author of tabu appears out of contact, and tabu had not been updated for several years, finally becoming unusable in 2019 as updates to other packages mean some of its patched code did not work as intended.
The package is not being actively maintained, however any major required fixes may be reported to the https://github.com/tabu-issues-for-future-maintainer/tabu repository and volunteers there (currently members of the LaTeX3 Team) will attempt to update the package with any fixes required.
https://tex.stackexchange.com/questions/471000/tabu-error-since-update
https://tex.stackexchange.com/questions/469282/xcolor-breaking-and-align-environments-inside-tabu
https://tex.stackexchange.com/questions/468948/longtabu-and-color-compatibility
https://tex.stackexchange.com/questions/430973/tabu-m-column-vertical-alignment-not-working-after-package-updates (Note that this is only a temporary fix reverting the change in array package m column implementation. A more complete fix would be to adapt tabu code to the new array.)
https://tex.stackexchange.com/questions/201510/what-is-the-difference-between-and-linebreak-in-cfoot