You may want to keep track of sales leads and interactions with people before they become customers. Customer Relationship Management (CRM) software can help you keep up with follow-ups. Most CRM software also helps with project management - allowing you to schedule and track multi-stage projects and collaborate with co-workers. I use mine to create a "to-do" list of recurring tasks for multiple clients and to keep a record of my interactions with them in one place. There is industry specific CRM for construction, field-service, and e-commerce, but a basic CRM can be useful for service businesses like real estate agents - and bookkeepers!
I like Insightly because it offers basic, affordable CRM and Project Management. There's a limited free version for two users that you can play around with. Contacts sync with QuickBooks. You can attach documents and forwarded emails to contacts. You can do bulk emailing and set up templates. The full paid version integrates with MailChimp for more design-heavy templates.
What Insightly doesn't have that some others do is invoicing, although you can see an organization's payment history pulled in from QuickBooks. Unless you have special invoicing needs (see construction) I think this is better done from QuickBooks anyway. Some pricier apps also have login portals so customers can see their order and payment history.
I use Insightly to keep track of various repeating tasks for multiple clients. I can see quarterly sales tax due dates on the calendar, and a list of all clients that need it on my task list. I can also look at a client and see a list of all the services I provide for them. And, I can see what I've finished and checked-off.
I recommend trying the free version of this software and seeing what it can do for you! I can help you get set up and running with Insightly.