I'm looking for software that lets me track conversations with vendors, clients, team members, etc. Each step of the conversation doesn't necessarily fall into a well-defined bucket (e.g. "converted lead", "planning", etc.) which is why I'm not sure a project management software or CRM software is exactly what I'm looking for. As of now I use an Excel spreadsheet but that's unwieldy.
I made a mockup of what I'm looking for:
Each step in the process/conversation would let me add custom notes, tags, and attachments, specify the date, and link each step to the previous and future steps. Ideally I'd be able to sort by date and make something akin to Gantt chart. I am OS agnostic between Windows/Linux and have no preference for a web application or a desktop application, but ideally I'd like something free and/or open source.
EDIT: These conversations or contacts happen across a variety of different media (email, phone, Slack, SMS, mail, in person, etc.) which is why something simply like "threaded email conversations" isn't sufficient.