Ghostfolio is awesome! Sorry for the plug, we are doing something similar with markets.sh
it's not open-source (yet) but we're giving you all the data of connected portfolios and bank accounts via api and it's free if you just want the data. Also we are investing a lot of time in asset matching and market data (even options are supported), something all the other tools we've tried fell short of (especially global stocks and multi currency accounts).