Why are three newly-downloaded, up-to-date, unrelated applications not starting: "not supported on this type of Mac" *not a PowerPC problem*
Problem identified. My machine only runs 32-bit at the moment. The latest versions of Tiled are 64-bit, and Gideros is all 64-bit. After a redownload and some minor glitches, Pixen seems to work fine. I downloaded an operational albeit outdated version of Tiled in the mean time. I really need to upgrade to 64-bit.
I guess I overreacted when all three had the same error, and indeed Pixen shouldn't have had the error (and no longer does). I didn't anticipate that Tiled would be 64-bit either. Oh well. Thanks for any and all input.