Grace is a free WYSIWYG 2D graph plotting tool, for Unix-like operating systems.

[2] Xvgr was originally written by Paul Turner of Portland, Oregon,[3] who continued development until version 4.00.

[5][6] Development of Xmgr was frozen at version 4.1.2 in 1998[3] and the Grace project was started as a fork, released under the GPL.

[7] The name stands for "GRaphing, Advanced Computation and Exploration of data" or "Grace Revamps ACE/gr"[6] Turner still maintains a non-public version of Xmgr for internal use.

It performs both linear and nonlinear least-squares fitting to arbitrarily complex user-defined functions, with or without constraints.