Dan Edwards wrote an interesting article on Medium yesterday about how No Divide manage projects.
If you're running an agency or even a freelancer it's worth reading or watching the video below which the article is based on.
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At amillionmonkeys we use git heavily, but rather than GitHub (Dan's preference) we host repositories with Beanstalk. This is purely because deployment with Beanstalk is so easy. In five minutes I can set up a repo invite contributors and have that deploying automatically to a staging server and deploying manually to a production server. This can be done using webhooks in GitHub, but can't be done as easily or quickly and given I do this at least once a week, that's vital.
Like No Divide, we also use Laravel when building apps. It feels the best option for PHP development at the minute. Instead of Forge, we use Fortrabbit as this is a one stop solution for version control, deployment and hosting and scales nicely.
When developing a workflow my advice would always be to find the tools that do the job and then pick the one which allows you to do the task in hand fastest and most easily. If you're past the point where you're doing websites for your mates, pay almost no attention to the cost of the service: when you charge per hour, time is money and subscriptions to any of these services will always pay for themselves.