My father used excel spreadsheets for the longest time. Each excel spreadsheet had separate tabs. Every time someone moved out he created a new tab. Also if he owed money on the property he had an overview tab. This worked great when he didnt have a lot of property to manage. Over the years however it doesnt work great when you start amassing an empire.
We looked to Buildium (online management) when we had about 60 tenants. Mostly because we didnt know about it sooner. The cost is $40/month for 40 units starting (increasing by $10 per 10 units). The norm appeared to be $1/unit per month with a minimum for most sites. You being a software developer might be able to use the free 30 day evaluation to come up with ideas on how you would want to create an online database. As for us (my father, brother, and myself) we now use it to maintain 100 tenants. It allows us to do credit checks ($15 basic credit check, eviction report, & criminal record), tenant payment portals (credit cards 2.7% fee & eCheck/ETF 50 cents), maintenance logs/requests, direct deposit of funds, P&L reports, Rent Roll Reports, email communication, and a ton of other useful features.
I use Quicken for my personal finances... But the Quicken Rental Manager, I didnt find very useful for myself. Also Quickbooks is great at helping me maintain my friend's service business but not as helpful at maintaining my property management.
Also I have an IT background and was looking for a database program to meet my needs. Hopefully that helps