It seems like Obsidian is not free, or if there is a free version of it?

Markdown noting app which exports to PDF and shows LaTeX
Hello everyone. First post in tech support.
I have been using Joplin and fed up with its accumulating errors. What alternatives that support similar features do you recommend? (ranking from most important)
- Can insert image
- Hyperlink by markdown language
- Supports LaTeX
- Supports Mermaid flowchart
- Export to PDF
- Can handle a lot of notes
- Windows and Android
- Migrate a chunk of markdown files all at once
Thanks a lot. Have a nice day :)
Eilf: Matrix stuff
- Determinant of a matrix
- Difference between inverse matrix and identity matrix and what are they?
- Eigenvalues
- Unitary or orthonormal matrix
- Diagonal matrix
- How to compute matrices?
Thank you in advance for answering anyone of them.

How to summarize a scanned PDF document by AI?
- Don't have ChatGPT
- OCR needed
- Preferably Android
Thanks.

How to find our career strength?
Long story short, it has been my 3rd time trying to graduate from college. How to find real strengths (aptitude that we can't change much)? Just want life to be easier. Thank you.
p.s. w Autism.

How to edit meta in epub that shows series in Calibre?
Edited meta in Calibre doesn't stick with the epub file. Is there any method to edit dc: meta in epub and the designated series under series shows up in Calibre?
Thanks and trying my best to explain the concept. If this is to vague please provide guide to explain more specific.
Do you mean decision-making on food or generally good decision-making? Not sure on what does it mean by reasonable problem solving, could we have some specific examples? Thank you.

Actions to avoid irreversible consequences?
As the titled mentioned, is there anything that we should do to avoid undesirable life consequences?
Sorry for lurking too much......how to use the bot?

Books on core exercises?
Preferably a structured graphic guides to initiate the habit. Fantastic if we can store the book for about 20 yrs in a bookshelf. Thank you.
Thank you. Although it may be irrelevant, do we need a VPN to avoid interception (what is it?) even if there is HTTPS?
Thanks and TL;OS (too long only skimmed). May I ask how to summon a summary bot here?
Noted with thanks. Btw how to change the modem w/o breaking fibre cables?
Why ISP doesn't know our activities when we use HTTPS?

Reading e-book w/ library account private?
Do ISP and library know what we read when we borrow books from platforms, such as Overdrive, with public library accounts? p.s. first post + app glitch can't enter new line.