Alternativa Bookisu za Microsoft Exchange Server sa licencom otvorenog koda

• Microsoft Exchange Server
  Sve platforme Windows Mac Linux Chrome OS Android iPhone Windows Phone iPad Android Tablet Web Self-Hosted Software as a Service (SaaS) PHP jQuery Windows Mobile Slack Microsoft Office Outlook Chrome Google Calendar Sunbird Google Apps Microsoft Exchange Server Apple Calendar
• Licenca otvorenog koda
  Bilo koja licenca Besplatna licenca Licenca otvorenog koda Komercijalna licenca