While not open source have a look at dhtlmx gantt, after starting to integrate it you’ll come to realise the sheer amount of work to get a Gantt chart working h

While not open source have a look at dhtlmx gantt, after starting to integrate it you’ll come to realise the sheer amount of work to get a Gantt chart working how you mostly expect it to. There’s just so many little features that you need to implement it’s mind boggling.