Rentastic is a software company designed to help real estate investors track their rental property expenses. Rentastic is built for real estate investors, BY real estate investors. The creators of Rentastic own multiple rental properties. As most investors soon come to find, accounting for all the different income and expenses can be a nightmare -- especially come tax time. While there are lots of different types of accounting software out there, too many attempt to be the end-all, be-all for every type of business.