I'm going to start a little index of useful solutions for Dynamics 365 - Add a comment with your recommendations and i will check them out and get them added

Do you have multiple files to upload to a record?

Drag and Drop Code from CRMXpress

https://crmdragndrop.codeplex.com/

Autonumbering on more than the standard entities? Complex rules?

eBECS AutoNumber for Dynamics 365

https://appsource.microsoft.com/en-us/product/dynamics-365/ebecsltd.b1617ac9-84b9-4db7-99d9-f7233bdb45fe

Multiple people working in 1 instance? Track the changes

Change Tracking Solution from Microsoft Labs

https://appsource.microsoft.com/en-us/product/dynamics-365/microsoft_labs.changetracking?tab=Overview

Do you have integrations setup Via Scribe

Integration Manager from Scribe

https://appsource.microsoft.com/en-us/product/dynamics-365/scribe-software.26438d1b-f5a3-41f8-86bf-002c388b9990?tab=Overview

Need to run scheduled workflows? fire in some FetchXML and away you go

Workflow Scheduler from Lucas Alexander

https://github.com/lucasalexander/AlexanderDevelopment.ProcessRunner