H3 ODST standalone build
The Halo 3 ODST Editing Kit includes a standalone build of that game (atlas_tag_test.exe). This build doesn't include network functionality and it intended for testing single-player maps. It includes AI debugging code not included in other published builds of the engine.
The standalone build is configured differently from the retail build of Halo 3 ODST that's part of MCC - bugs or features found in one might not be found in the other. For that reason maps should always receive final testing as map cache files loaded by MCC itself.
It's pretty much identical to Halo 3 Standalone so please refer to that page for further info on hotkeys and features.