SIT is a Stuffit archive file. These were common on Macs. While the PC world mostly used WinZip and ZIP files, Macs mostly used Stuffit and SIT files.
To expand SIT files you need either Stuffit, or the free version of it (Stuffit Expander). As you have a 68000 Mac AFAIK the last version you can run on it is 4.5 (4.0 under System 6). Please note that SIT files made by later versions (like Stuffit 5 IIRC) can not be opened by earlier versions, so you need to make sure it can be opened by the version of Stuffit you are using (or find a Mac/emulator running a later version of Stuffit to expand it).
SEA is a Self/Stuffit(?) Expanding Archive. It is like a SIT file, but you should be able to open it like a normal program, and it will decompress itself.
For making Mac compatible disks (1.44mb, not 800k or earlier) I have had luck in the past using HFSExplorer. It is getting on in years, but I think it still runs on Windows 7/8.
To expand SIT files you need either Stuffit, or the free version of it (Stuffit Expander). As you have a 68000 Mac AFAIK the last version you can run on it is 4.5 (4.0 under System 6). Please note that SIT files made by later versions (like Stuffit 5 IIRC) can not be opened by earlier versions, so you need to make sure it can be opened by the version of Stuffit you are using (or find a Mac/emulator running a later version of Stuffit to expand it).
SEA is a Self/Stuffit(?) Expanding Archive. It is like a SIT file, but you should be able to open it like a normal program, and it will decompress itself.
For making Mac compatible disks (1.44mb, not 800k or earlier) I have had luck in the past using HFSExplorer. It is getting on in years, but I think it still runs on Windows 7/8.