Developers: What is your workflow for developing for Web AppBuilder in a team environment?

[GavinRehkemper]

I'm interested to hear from anyone who is developing custom widgets or themes and are working on them with teams:

1. Are you using source code management (GitHub, SVN, TFS, etc)?
2. Are you using any processes/tools (grunt, gulp, etc)?
3. Any other stories/best practices you've found? What are your workflows?