It is generally considered that there are 6 types of informal reports. These are as follows:
- Information Reports
This usually follows the format of introduction, main body and conclusion. These reports are usually just data based, and used to stack necessary data e.g. Daily activity.
- Progress Reports
These are progress-based reports that satisfy questions in the vein of, 'is anything in addition needed to complete the activity?' or 'is everything running according to plan?'. It is essentially a troubleshoot checker.
- Recommendation Reports
These reports are largely oriented around analysis. This is the trouble shoot report, offering solutions to problems and evaluating pros and cons.
- Feasibility reports
How feasible is the project? These reports suggest whether it is likely to fail or succeed, and whether it's wise to invest (further) capital.
- Minutes of Meeting
This is a report that accounts for all details of the meetings, including date, time and discussions.
- Summaries
This is the final evaluation of the entire project, and aims to provide an overview of performance.
I hope this helps.