If you find a bug in Calc, send e-mail to bug-gnu-emacs@gnu.org. There is an automatic command M-x report-emacs-bug which helps you to report bugs. This command prompts you for a brief subject line, then leaves you in a mail editing buffer. Type C-c C-c to send your mail. Make sure your subject line indicates that you are reporting a Calc bug.
If you have suggestions for additional features for Calc, please send them. Some have dared to suggest that Calc is already top-heavy with features; this obviously cannot be the case, so if you have ideas, send them right in.
At the front of the source file, calc.el, is a list of ideas for future work. If any enthusiastic souls wish to take it upon themselves to work on these, please send a message (using M-x report-emacs-bug) so any efforts can be coordinated.
The latest version of Calc is available from Savannah, in the Emacs repository. See https://savannah.gnu.org/projects/emacs.