Getting our systems talking to the ones you already run, so a number entered once does not need entering again somewhere else. Most of the value in new software is lost at the seams.

Anything with an API or a file drop: Sage, payroll systems, banking files, municipal financial systems, and the spreadsheet somebody maintains by hand.
Data entered once and read everywhere, instead of three systems disagreeing about the same figure.
The copying between systems that eats an afternoon a week, and introduces the errors nobody can trace later.
Integration rather than replacement, so a system that does its job well is left alone.
Documented, authenticated connections between our products and yours, built to survive the other side changing without warning.
Where an API does not exist, scheduled imports and exports in the format the other system actually accepts.
Posting to the general ledger properly, including the mSCOA segments municipal systems require.
When a sync fails, somebody is told and the record is queued, rather than the failure being discovered at month end.
What lives where, which system owns each field, and what has to move in which direction.
The exact shape of what is exchanged, written down so both sides can build against it.
Built against a copy of your data, and reconciled line by line before it touches production.
Alerting on failures, because a silent integration is one nobody notices has stopped.