Well, depending on what you need to do, you could use SQL Server Agent to schedule operations and T-SQL procedures within the database itself. You could also use the Windows Task Scheduler on the host to run batch or PowerShell jobs, if you are in a VPS or dedicated server environment. Hosted environments might also offer some sort of scheduler, but I'm not really familiar with that.

I wouldn't recommend scheduling time-critical processes within mojoPortal custom code, because there is no guarantee that the web server will be up and running at any given time (hence the need for a keep-alive solution for low-volume sites). But if timing is not critical, and you have the ability to do your own development (or contract for it), you might also leverage the Task Framework in mojoPortal to set up a long-running job that can be resumed, and does something at defined intervals. For instance, if you are confident that someone is signing into your site pretty much every day, a User Sign In Event Handler could check for the presence of a running job, and if not, schedule a new one to last for 24 hours. That's just an example idea.

Hope that helps,

Jamie