SharePoint - differing (outside) topics that help to transfer across

This is a great list of topics that definitely help you with SharePoint - good if you've worked with them before:

1. Competitor Web Content Management products - particularly if they implement Cross-Authoring and Publishing
2. Competitor Enterprise Content Management - Records Management products e.g. Documentum etc ... 
3. Some of the more heavyweight Business Intelligence Competitors - a list can be created by a comparison of the functionality - but later on as I run into them:
• On that point I am not that impressed with Crystal Reports and that competitor Microsoft Product I'm sure you can all fill in - and I am not blown away by Tableau or Power BI either
4. SharePoint Security can and does make heavy use of digital certificates - make sure you have a glance at https://en.wikipedia.org/wiki/Public_key_certificate ~ some places that Certificates are used (not to forget that Digital Certificates can be also used to sign Office documents): 
• Internal connectivity
• External connectivity
• Connections between SharePoint Farms (i.e. trusts between SharePoint Farms)
• Connections between SharePoint and Exchange / Skype for Business 
• On-Premise SharePoint App Store
• Claims Authentication integrated with SharePoint 
• etc ... 
5. A bit of starter SQL Server Analysis Services in Business Intelligence - Obviously SSAS is a big topic - so you can start on the bits common to both SharePoint and SSAS ...
• In fact that might not be a bad way to start learning SSAS.  
6. Obviously if you're connecting to non-Microsoft data sources with say Enterprise Search or the Business Connectivity Services  it does help if you know some of the basics:
• Non major Microsoft data sources include Oracle, Lotus Notes etc ...
• FYI - the list of (fairly common) Microsoft sources includes Access, SQL Server, File Server (for Enterprise Search) etc ...