The Tcl and Tk source repositories can be found at
The version control system used for these is Fossil.
The remainder of this page follows Fossil's generic Quickstart Guide , modified to suit Tcl/Tk development.
Prebuilt binaries for the major platforms (Linux, OSX, Windows, BSD) are available at http://www.fossil-scm.org/download.html Building it yourself is of course possible as well.
Fossil works with repository files (a database with the project's complete history) and with checked-out local trees (the working directory you use to do your work). The workflow for Tcl and Tk looks like this:
First, clone the repository
fossil clone http://mirror1.tcl.tk/tcl tcl.fossil fossil clone http://mirror1.tcl.tk/tk tk.fossil
We are using mirror1 because the repositories are large and http://core.tcl.tk/ is bandwidth-limited.
Then create local checkouts to work with (using Tcl as example):
mkdir /somewhere/tcl cd /somewhere/tcl fossil open /wherever/you/have/tcl.fossil
Now you have the most recent revision of Tcl's trunk (ex-CVS HEAD) in the directory. Hacking can commence.
For those which have worked on the core before, using CVS, please see the Fossil vs CVS Commands.