Good question, as an investor I'm always looking for better apps and technology to acquire better information and then make better decisions, that net me more profit. I also want the tech to do most of the work if possible. That's why my phone is probably my most valuable tool. I use all the real estate websites like Zillow, Redfin, trulia, and realtor.com because they all tell me different pieces of information, for instance realtor.com gives me an idea on neighborhood noise and crime. Rentometer.com is critical because along with the above websites I get a sense of the rental estimates of a neighborhood. Then the BP calculators or a spreadsheet to make sure I'm making a good buy. I also search Homedepot.com to make sure contractors material estimates are making sense.
All of this to say I'm using a few simple tools right now, to make sure I'm buying right. As my rehabs and deal finding become more complex I'll upgrade to Propstream and project management software, but I'm not at that level yet. I hope this is useful for you.