Technology Stack - What software are you using and how do they work together?

We actually used this as our RCS Influencers topic this month.  We asked what their technology stack is, (see their responses here), we wanted to know what software they were using for their business and how it all works together. I have been in the roofing business for 42 years and some business software is so amazing and some things are still done with pencil and paper.  What say you?