What Rental Management Software to use

My wife and I own and manage 6 units. We have just bought another block of 7 units. Currently we just use spreadsheets etc. to manage the rent due and arrears. We really need software to ensure we keep on top of this with the extra units. We just want to enter rent received each week and for the software to report who is behind in rent and by how much. What would you recommend.
I had a play with rentmaster. All I really want to do is enter the rents paid per week, and then report on arrears. Rentmaster seems quite cumbersome and slow to enter rents paid.
Rentmaster is a fully blown pm system which handles different owners, disbursements to owners, extra charges like water rates and complies with fair trading requirements for real estate agents so it has more detail than you may need (unless each of your properties is owned by different entities).

other packages include propertypro (off the market now) or Posh.