10 open-source alternatives for small business software

Email: Thunderbird
Email is the primary method of communication for most businesses. There are a number of paid and free email clients available, but Microsoft Outlook is one of the most widely used. Outlook is part of the Microsoft Office Home & Business package, as well as the more expensive Microsoft Office Professional suite, or it can be purchased separately for $95.

Calendar: Lightning
Another function that most businesses rely on Microsoft Outlook for is the calendar. With all your appointments, conference calls, sales meetings, and deadlines, you need a robust calendar tool to manage your days.