What's the best community platform for launching a new topic-based forum with low-friction posting?

If your priority is low-friction posting for a new topic-based forum, the best choice is usually:

Discourse

It’s the strongest all-around option for launching a modern community forum because it’s:

• Easy to post in from desktop and mobile
• Good for topic-based discussions and categorization
• Highly discoverable with tags, categories, and search
• Active and modern compared with older forum software
• Flexible enough to grow with your community

Why it fits “low-friction posting”

• Users can reply by email or browser
• Registration can be lightweight
• The UI is clean and familiar
• Social login is easy to add
• Mobile experience is solid

Good alternatives depending on your needs

Circle

Best if you want a more polished, community-product feel with memberships, courses, or paid access.
Downside: not as classic/forum-like and can be less ideal for deep topic threading.

Reddit-style custom stack / Flarum

Best if you want a very lightweight forum experience.

• Flarum is simple and fast
• Easier onboarding than older forum platforms
• Less feature-rich than Discourse

Discord / Slack

Best for very low-friction conversation, but:

• Not great for long-term topic organization
• Harder to search and archive
• More chat than forum

My recommendation

• Best overall: Discourse
• Best for simple/clean forum UX: Flarum
• Best for membership/community business model: Circle
• Best for chat-first communities: Discord

If you want, I can also give you a decision table comparing them for:

• ease of posting
• moderation
• SEO
• mobile experience
• cost
• self-hosted vs hosted