You need to pay for Obsidian if and only if you use it for revenue-generating, work-related activities in a company that has two or more people. Get a commercial license for each user if that’s the case. Non-profit organizations do not need commercial licenses.
For all other uses, you can use Obsidian for free forever.
To support our development, you can pay for one-time Catalyst licenses to get early access to new Obsidian versions, but it’s completely optional. You can contribute more via Obsidian Unlimited if you wish.
Expanding:
COMMERCIAL USE
Commercial Use Licenses are required whenever Obsidian is being used for work for a business with two or more personnel. Sole proprietorships or other one-person organizations do not require a Commercial Use License. Work for educational purposes does not require a Commercial Use License.
Commercial Use Licenses must be purchased on an annual and per user basis. Commercial users must purchase at least as many licenses as the number of people who will be using Obsidian.
Lots of FAQs addressing specific “is this commercial?” questions, too.