Chris Sears and Dan Sears wrote the original XBoard. They were
responsible for versions 1.0 through 1.2. The color scheme was taken
from Wayne Christopher's XChess program.
Tim Mann was primarily responsible for XBoard versions 1.3 through 4.2.7, and for WinBoard (a port of XBoard to Microsoft Win32) from its inception through version 4.2.7.
John Chanak contributed the initial implementation of ICS mode. Evan
Welsh wrote CMail, and Patrick Surry helped in designing,
testing, and documenting it. Elmar Bartel contributed the new piece
bitmaps introduced in version 3.2. Jochen Wiedmann converted the
documentation to texinfo. Frank McIngvale added click/click moving,
the Analysis modes, piece flashing, ZIICS import, and ICS text
colorization to XBoard. Hugh Fisher added animated piece movement to
XBoard, and Henrik Gram added it to WinBoard. Mark Williams
contributed the initial (WinBoard-only) implementation of many new
features added to both XBoard and WinBoard in version 4.1.0, including
copy/paste, premove, icsAlarm, autoFlipView, training mode, auto
raise, and blindfold. Ben Nye contributed X copy/paste code for
XBoard.
In a fork from version 4.2.7, Alessandro Scotti added many elements to the user interface of WinBoard, including the board textures and font-based rendering, the evaluation-graph, move-history and engine-output window. He was also responsible for adding the UCI support.
H. G. Muller continued this fork of the project, producing version 4.3. He made WinBoard castling- and e.p.-aware, added variant support with adjustable board sizes, the crazyhouse holdings, and the fairy pieces. In addition he added most of the adjudication options, made WinBoard more robust in dealing with buggy and crashing engines, and extended time control with a time-odds and node-count-based modes. Most of the options that initially were WinBoard only have now been back-ported to XBoard.
Michel van den Bergh provided the code for reading Polyglot opening books.
Meanwhile, some work continued on the GNU XBoard project maintained at savannah.gnu.org, but version 4.2.8 was never released. Daniel Mehrmann was responsible for much of this work.
Most recently, Arun Persaud worked with H. G. Muller to merge all the features of the never-released XBoard/WinBoard 4.2.8 of the GNU XBoard project and the never-released 4.3.16 from H. G.'s fork into a unified XBoard/WinBoard 4.4, which is now available both from the savannah.gnu.org web site and the WinBoard forum.