Our website provides a free download of SymbioticReminder 0.9 for Mac. The application lies within Business Tools, more precisely Project Management.
From the developer:
There are only two dialog boxes. The first one asks you WHAT you want to be reminded of and the second one says that you will be reminded in 30 minutes (or in five or 4000 if you want). That's it. After 30 minutes you will be reminded (or after five). The only application you need is iCal running in the background. So you have a new invisible reminder, a symbiotic reminder.
You may want to check out more Mac applications, such as Project Timer Pro, Onepoint Project or Open ERP, which might be similar to SymbioticReminder.