I know it's been 4 years, but Housters has to be mentioned here, as it has all of the features the original poster asked for. It has a web site (housters.com) and Android/iOS mobile apps that are all cloud-synced. It has the basics you'd expect like tracking tenants' unpaid rent, managing to-do lists, accounting, and reporting, but also has some other goodies like tenants being able to make online rent payments to you through Housters and contractors being able to login to Housters and update your to-do list tasks that you assign to them.