Any recommended application for this case?

Hi!
I don't know how to describe this. OK, let's suppose that I have a small enterprise (between 10 and 15 employees)

I need an application to help me (and them) schedule their work, remind them of things to do, and display alerts about such tasks.

I can't think of other things right now, because this is all that matters now, the reminders, and the to-do lists.

Thanks in advance.

 

Exchange server with shared calendars and outlook on the desktop?

 

Thanks. I already know about Exchange Server, but it's not cost-effective in my situation. Don't you think so?

I need a small lightweight application for my very small LAN.

Thank you again.