Office365 is a pretty good solution from Microsoft which offers entire MS office to be available on cloud to access from anywhere and work from anywhere, but this is pretty much expensive and you have to pay per user, per month recurring amount to avail and use this service.
Well for all open source lover there is a good news for you, After extensive research I am found a solution that is perfect open source alternative of Office 365, yes this is TeamLab office which is totally free and can be hosted on any Windows server running machine.
What you can do with TeamLab Office?
TeamLab Office comes with key modules like Documents, CRM, Projects and Mail, each module of TeamLab Office has in depth functionality like in Documents module you can manage your entire document related work like a Document management system similarly in CRM you can manage customer data, in Projects can maintain projects, in Mail can manage all your email communications. It’s all in one open source office solution. for information check out its website.