I already developed several apps in LibreOffice Base in conjuction with PostgreSQL so you can work with diferent clients at the same time. I can use images, tables, reports, sofisticated queries, store procedures in Postgresql that can be viewed and used in LibreOffice. My systems work over any OS windows, linux or MacOs, the postgresql server can be also installed on any OS. The system don't slow down over time as the native HSQLDB. Have isolated transactions so if the computer crashes the data is safe. Data can be linked to calc or writer. I have 10 years of experience since OpenOffice was from Sun.