Edit: I tried typing in the link itself into a new tab (appinv.us/aisetup_windows), and it worked! 
It downloaded a file called "MIT_App_Inventor_Tools_2.3.0_win_setup.exe" with the correct icon.
[I also founds another thread (below) that gives another solution:]
Http://appinv.us/aisetup_windows - the site doesn't work
(Also, I am on Windows.)