Server

Open a PowerShell instance with elevated rights.
In the PowerShell window, type: Import-Module ServerManager and hit [Enter].
When that completes, enter the command below for the OCS server role(s) needed:

Archiving Server:
Add-WindowsFeature AS-NET-Framework,Desktop-Experience,NET-Framework-Core,MSMQ-Server,MSMQ-Directory,RSAT-ADDS

Communicator Web Access Server:
Add-WindowsFeature AS-NET-Framework,Desktop-Experience,NET-Framework-Core,MSMQ-Server,MSMQ-Directory,RSAT-ADDS,WAS-Process-Model,WAS-Config-APIs,Web-Basic-Auth,Web-Common-HTTP,Web-Digest-Auth,Web-HTTP-Logging,Web-HTTP-Redirect,Web-ISAPI-Ext,Web-ISAPI-Filter,Web-HTTP-Logging,Web-Mgmt-Compat,Web-Mgmt-Console,Web-Request-Monitor,Web-Windows-Auth

Edge Server:
Add-WindowsFeature AS-NET-Framework,Desktop-Experience,NET-Framework-Core

Front-End (Standard Edition) Server:
Add-WindowsFeature AS-NET-Framework,Desktop-Experience,FS-FileServer,NET-Framework-Core,MSMQ-Server,MSMQ-Directory,RSAT-ADDS,WAS-Process-Model,WAS-Config-APIs,Web-HTTP-Logging,Web-Mgmt-Compat,Web-Mgmt-Console,Web-Static-Content,Web-Windows-Auth

Front-End (Enterprise Edition) Server:
Add-WindowsFeature AS-NET-Framework,Desktop-Experience,NET-Framework-Core,MSMQ-Server,MSMQ-Directory,RSAT-ADDS,WAS-Process-Model,WAS-Config-APIs,Web-HTTP-Logging,Web-Mgmt-Compat,Web-Mgmt-Console,Web-Static-Content,Web-Windows-Auth

Mediation Server:
Add-WindowsFeature AS-NET-Framework,Desktop-Experience,NET-Framework-Core,MSMQ-Server,MSMQ-Directory,RSAT-ADDS

Monitoring Server:
Add-WindowsFeature AS-NET-Framework,Desktop-Experience,NET-Framework-Core,MSMQ-Server,MSMQ-Directory,RSAT-ADDS

These commands are largely based on the Server 2008 R1 blog entries here and here.

If my blog software shows the Add-WindowsFeature items on multiple lines, cut and paste the commands together onto one line inside PowerShell.

Note: If you install .NET Framework 4.0 before installing OCS, the OCS setup program will complain that .NET Framework 3.5 is missing, even if .NET Framework 3.5 has been installed. Thankfully, you can uninstall .NET Framework 4.0 if you bump into this issue and the setup program will behave normally. Thanks go out to Mark Rineck for discovering this.

Note 2: As mentioned on other sites, Web-HTTP-Logging is technically optional, but makes debugging IIS and OCS much easier if available.