Many are found on this site (and there are many), eg.
but not all are on this site. Many of the teams (eg. kernel, desktop etc) provide their own pages dealing with their own areas of development, on this site.
For a changelog you could always view
which you’ll note get updated somewhat regularly during the cycle (view top right and you can see 24 edits thus far, this history lets you explore further too), but expect that detail to change irregularly whilst we’re still in alpha and become more complete as beta approaches.