By RAW, you could technically argue that any cyberprogram goes, including the 500 nuyen one from Data Trails and yes, even agents.
RAW, as usual, is annoyingly inconsistent. So at our table, we just said you can buy the Program Carrier for 750 nuyen and it includes a common use program, or you buy a separate program at the normal cost to be hardcoded to the module.
Under these rules, Virtual Machine and Agent programs are both allowed, but you can't run an Agent on a virtual machine slot.
These are all house rules, though. RAW is, as mentioned, lacking in this case...