There are others too... http://appfolio.com http://buildium.com http://propertyware.com http://tenantfile.com and others. This isn't a new idea, people have been using property management software for years. We have just taken a slightly different approach to implementation with automation and communication between the two parties, landlord/tenant.
Our ability to automate a lot of the managers monthly activity sets us appart. Rentmonitor currently only does 'after the fact' accounting, meaning tenants still have to bring in a check or pay an e-bill. Our system allows tenants to pay electronically through their site and submit work orders.
So the time savings w/ our software can be huge. As well as payments getting 'lost' or not recorded doesn't become an issue anymore.