Seeking advice for an entry level customer categorization platform

Hi and apologies if this isn't the correct place to post this.

I own a small tech startup and have found that I need a way to get better organized and a friend suggested asking you guys. What I'm looking for is something that I can use to input my customer information such as Name, Address, subscription date, subscription expiration date, etc.

We're fairly small and new so some form of freeware would be extra helpful.

Some form of rule based alerting would be awesome as well.

Any ideas for software or suggestions for software developers to contact?