Free Investment:
1. Education
2. Network
3. Time
4. Health
5. Cultivation or skills
6. Financial Literacy
You highlighted key points that is very important in our daily lives and investment wise.
These things are not actually free, but we can dedicate ourselves with these factors that we have in our possession to get something good for ourselves especially
Education which is the only investment you can have for free in the internet and forums like this one and social media.
With this, I believe you OP.