Hi,
I use YUNOHOST for my personal use. Being a novice, I find it easy to use and maintain.Thank you for bring self hosting to the average users.
I have teamed up with a couple of friends to work on a startup idea. We need a project management software to help us on our journey. I am looking into using the community edition of Open Project (https://www.openproject.org/).
I would appreciate your opinion on whether Is it possible to use Open Project on a YUNOHOST instance?
Hellow !
Thank you for using YunoHost 
As for any apps which isn’t packaged yet : you can probably install the app “manually”. That is : following the instructions of the project (c.f. https://www.openproject.org/download-and-installation/#installation ). That will require some basic or advanced knowledge of system administration depending of the complexity of the app. I don’t have a clear idea of how complicated it is how their instructions include stuff like SSL and mail config which are already done on YunoHost.
Though keep in mind that doing so, your app won’t be integrated with YunoHost (e.g. SSO integration, backup management) though maybe you don’t need that. To do so you need to properly package the app (c.f. https://yunohost.org/#/packaging_apps ). (If that’s of any interest to you, there are people in the dev team offering app packaging as a service - or general assistance related to YunoHost).