I use Outlook, OneNote, and Excel. With Outlook, I create folders and rules to separate my emails as they come in. I also use OneNote to create a tab for each of my clients that contains all the client information I might need. Additionally, I use Excel to maintain a spreadsheet as my to-do list. As tasks come in, I add them to my list to ensure I don't forget anything. Once a task is completed, I highlight the cells in green to indicate that it's done.