Download
First things first: read the Installation Manual for 2.4. There's more to installing WeBWorK than just downloading a tarball. But if you just can't wait, or want to get a look at the code, read on...
WeBWorK can be downloaded from SourceForge or checked out of CVS. We recommend that you install WeBWorK from CVS, since you can get more up-to-date code that may contain bug fixes that haven't been released yet. It also makes updates easier.
Download WeBWorK and PG using CVS
You most likely want the bugfixes branch for the current version. To grab that from CVS, type the following:
cvs -d :pserver:cvs.webwork.rochester.edu:/webwork/cvs/system co -r rel-2-4-patches webwork2 cvs -d :pserver:cvs.webwork.rochester.edu:/webwork/cvs/system co -r rel-2-4-patches pg
See the Installation Manual for 2.4 for details.
Download WeBWorK and PG from SourceForge
http://sourceforge.net/project/showfiles.php?group_id=93112
Release notes and current version
The current version of WeBWorK is 2.4.5. The current version of the PG Language is 2.4.5. The latest stable branch, which includes bug fixes and features since the release 2.4.5 is rel-2-4-patches. (The release tag rel-2-4-dev has been discontinued.)