[Shinmon]

I use obsidian to keep track of most things that are unstructured. This is where I keep my todos, my personal project documentation, meeting notes, etc.

For managing clients (or contacts really) I would use a table or a spreadsheet. This is you most important asset to be honest. Separate clients, leads and other contacts in extra lists. Keep track of when you met them, how you met them, their email, company, phone number and any random comment to understand what you can ask them for. Also, connect with other freelancers and try to help each other out.

For time management I use clockodo although there are many options: toggle, clockify, ... They all have their pros and cons.

Payments shouldn't be too complicated. As a solo contractor you will likely only have 1-3 clients at the same time. So it shouldn't be too hard to keep track of incoming payments. When you bill them, add a calendar entry when to check if it has been paid.

Generally, don't over-complicate things. Use simple tools as long as you are a solo contractor.