Implementing an open source enterprise structure?

Question

open source

Good afternoon, can someone suggest the following open source replacement:
Exchange + outlook + sharepoint + skype for business, you will have to implement everything yourself, and you need to tie the whole thing to AD, the number of users is ~ 150.

Answer 1

And AD on what will be? On Windows? If so, then it makes sense to fence the garden - all the same, licenses will be needed. Moreover, if the garlic - 150 client :)
If there is Samba / IPA - then again there is a fork - what you need from Exchange. If groupware-chips (calendar-tasks-notes-common address book) are not needed - SMTP server + IMAP server to taste, you can set a web muzzle if you used OWA. If groupware features are needed - Zimbra, Zarafa - they have community versions, although in this case you will have to do the import of mail yourself. Well, Zimbra's mail client is incredibly ugly. But "almost exchange". There is also SoGo, but I have not looked at it, I just know that there is.
Skype is free, as for "for business" - carefully analyze what it gives you and whether you need it.
Sharepoint - they don’t use it for anything, so you can’t give general recommendations here, you need to know what kind of tasks are being solved, otherwise maybe a banal telephone directory is being formed there and that’s it :)

Answer 2

For mail, you can take iRedMail. For the address book from what I used, ownCloud / nextCloud are able (they can do a lot of other things). It seems like both of these things can be connected to Open LDAP, but I have not worked with it and have no idea how it is all together. For chats and calls, you can take Rocket.Chat, there are also some plugins for ownCloud with similar functionality / integration.