OneNote is a note-taking application with real-time sharing and collaboration features. It comes free within an Office 365 subscription.
Paylocity is a unified human capital management platform with robust payroll and HR tools. Its monthly fees reportedly start at $2 per employee.
ADP Payroll offers payroll and tax services for businesses of all sizes. Reported pricing ranges from $10 to $23 per employee per month.
Slack is a team communication and collaboration app that helps users streamline their workflows. Prices range from $0 to $15+/user/month.