Subreddits starting with O

Oakland, California: local discussion.

Athletics fans: games, news, and discussion.

Raiders fans: games, news, and discussion.

Objective-C programming.

Objectivism and the philosophy of Ayn Rand.

The Elder Scrolls IV: Oblivion.

Rare and obscure media.

The OCaml programming language.

Support for people with OCD.

The oceans: science and conservation.

Oculus / Meta Quest VR.

Living off-grid: power, water, and homes.

Get something off your chest.

Fans of Odd Future: music, news, and discussion.

Ohio: news and discussion.

Ohio State football.

The OkCupid dating site and online dating.

Oklahoma: news and discussion.

Old and historic maps.

Cool photos from the past.

Olympia, Washington: local discussion.

The Olympic Games: events, athletes, and news.

Omaha, Nebraska: local discussion.

Discussion of Once Upon a Time.

People who had one job and failed at it.

Jokes told in a single line.

Short stories told in a single paragraph.

Fans of the One Piece manga and anime.

Men's issues and discussion.

Learning online: courses and resources.

Ontario, Canada: news and discussion.

Open, inclusive Christianity.

OpenGL graphics programming.

Open-source software.

Open-source games you can play and contribute to.

OpenTTD, the open-source transport game.

Opera: productions and recordings.

The Opera web browser.

Support for recovery from opioid addiction.

Orange County, California.

For people who play in orchestras.

Oregon: news and discussion.

Organic gardening methods and tips.

Origami models and folding instructions.

Baltimore Orioles fans.

Orlando: news, events, and local discussion.

The scientific study of birds.

Operating system development.

For students at Ohio State.

macOS help and discussion.

Ottawa: local discussion.

Ottawa Senators fans.

Otters: photos and videos.

The outdoors: hiking, camping, and nature.

For Redditors over 30.

Overclocking computer hardware.

Owls: photos and facts.