Have you considered creating one (or several) spreadsheets to track your clients/groups using Microsoft’s new version of Excel? This updated version is a part of their Office 365 bundle which can grant you access to your documents from virtually anywhere you have the internet. There might even be tracking templates available for you to use at no extra cost.
Here’s a direct link to more info from Microsoft Office’s official site:
I hope this helps and best of luck to you in your search!