Xcode 3.1.1 Release was released on 23 Jul 2008 and requires macOS 10.5+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/xcode_3.1.1_developer_tools_preview_1/xcode311_9m2517_developerdvd.dmg.
Release notes are located at https://download.developer.apple.com/Developer_Tools/xcode_3.1.1_developer_tools_preview_1/about_xcode_3.1.1_tools.pdf.