It's PHP and Javascript. I just added a small note in the 'Easy Installation' section on the front page. I'll try think of a better way to present it going forward.

Can you expand on the requirements? What PHP modules are expected or needed? What's the minimum version of MySQL?

For a self-hosted app, I would want more information about it before I considered buying it sight-unseen. Maybe consider providing a small PHP script that I could run on my server to validate all the requirements?

It's built for the lowest common denominator. Literally all you need is PHP 5.4+ and Mysql 5+, and curl. There aren't any required modules for basic usage but you may want smtp (if you don't want to use built in php mail function). Cron for recurring tasks, which isn't required for basic usage, but for things like recurring invoicing and reply by email. I'll add a new page in a couple of minutes that lists all the details.

Also agree about a validator script. I'll work on that too.

no orm .. i mean postgresql support ?

Or easier provide a Dockerfile

That's not easier at all. Not for the moderately-technical small-business owner that the parent comment discusses, or indeed many other (mostly shared hosting) scenarios?

Fair point. For me it's easier :P