QField is an open-source Android based mobile data collection and/or viewing application that is tightly integrated with QGIS.
QGIS is used to set up the project using standard QGIS tools.
If the layers in your project are stored in a PostGIS database and a mobile data connection is available then changes made in QField are made directly to your database and visible in real-time to anyone that has a client to your database. This, in my view, is the mobile data collection killer app.
QGIS symbology is recreated in QField.
QGIS edit widgets are used to create data entry forms in QField.
If a relate is set up in the QGIS project then the same relates are used in QField to create child records, such as plant composition associated with a point.
If print layouts are created in the QGIS project then those print layouts can be used to generate PDF documents on the device and emailed to project managers or clients.
You can collect photos with your mobile device and store a path to the file in a text field.
If no mobile data connection is available QGIS can be set-up to work off-line. Of course you will be collecting data locally on the device and then have to sync it to the database and the data will no longer be available to others in real-time. This is very easy to do using the Qfield Sync plug-in in QGIS and the details are explained in the course.
QField is not perfect, but it is very powerful and as an open-source project you can hire someone to add functionality if you need it. Or do it yourself if you are capable. Chances are it will work for you without modification and if that is the case it can save your organization a lot of money on per-user fees and subscriptions.
You can purchase this course which will explain all the details from Udemy.com
Check out my other Open-source GIS courses.
An overview of the entire process (and one lecture of the course) can be viewed below.