Client Project Frontend Suggestions/Help

I run a small business making custom coded plugins (not for wordpress or other CMS platform hence asking), and I am looking for a plugin that can use a front end page for clients to see the project, and then open that project and download files from there. And submit questions etc… and a billing section would help, but not necessarily required. I would want to open these projects manually. I have had a look, but I’m not really sure what to search for!

I wondered if anyone knows of a plugin I can use to do this, or something very similar?

Any help is welcomed.

Thanks.