I like knitting and crochet, if you go on car boot sales you can often find a lot of balls of yarn almost free, and there are so much things you can do, for you or as gifts!

Shoplifting can be both fun and profitable

I love going on hikes or nature walks. Some great free apps are Merlin (for identifying bird calls) and Seek (for identifying plants and animals). All completely free aside from getting to to trail, but even in city parks it can be pretty fun. A good pair of binoculars is a great addition if you have the $$.

Im a big fan of calligraphy. It can be free using just a pencil and paper that you have. But it is more fun if you spend the $35 on marker paper and a calligraphy marker.

Research the shit out of something you are interested in. Go down all the rabbit holes you can find. Compile it into a simpler, better understood synthesis. Convert it into a YouTube vid and deploy. I'd watch anything if well researched.

Geocaching

I have spent most of my life partner dancing. Almost every organized dance I've gone to has been volunteer run. So while it's not technically free, it's pretty easy to get in for free if you ask nicely and trade an hour of your time.

Do you have a working laptop or desktop? Learn to code. Actually code none of that vibe code bullshit. Making games is fun and rewarding and has an amazing community.

Running costs a pair of shoes every now and then and extra laundry detergent but otherwise free. Like any other hobby you absolutely can spend tons of money on it but it's not required.

Runkeeper is a free app where you can log down your runs but a casio watch with stopwatch is good enough if you know the distance.

Also, contrary to what a lot of people think you don't have to push yourself, you can just be easy running (chill jogging) and still make massive gains in endurance, speed, physical health and mental health. Depending on your starting point brisk walking can be sufficient to get started and then transition to "let me just jog a bit" when you feel like it and still have massive gains.

You can even combine it with other hobbies like audiobooks, music and/or podcasts.

Running feels to me like "cleaning the pipes" of the body that's relaxing and makes the remainder of the day a bit more enjoyable.

Recreational Public Masturbation and it’s almost essential sister-hobby of Eluding Law Enforcement While Maintaining an Erection.

Hiking, walking and swimming are all free for me.

Kicking the football around with a friend at the local park (need a football).

We also have a free to use tennis court and have cheap tennis racquets and a cheap pickle ball set we use there.

local library, i read extensively and have a gazillion ebooks but i like to browse the library shelves for gems.

check with your local authorities, maybe something there as well,? eg local community groups you can help eg here in Australia there's places like Landcare where you go help rehabilitate nature with like minded folks.

From a similar post recently:

Inexpensive, and little setup, with no steep learning curve?

Off the top of my head:

• singing
• drawing
• playing a tin whistle
• dorodango
• dexterity games (card flourishes, astrojax, yoyo, pen spinning, etc.)
• reading
• kumihimo
• customising things with paint markers
• yoga
• whetstoning
• writing (prose or poetry)
• journaling/journalism
• cross stitch/embroidery
• jelqing
• rock/object balancing
• meditation
• knife throwing
• macramé (using beading floss)
• playing the spoons
• whittling
• eating
• scrimshaw
• nålbinding
• henna tattooing
• primping
• cloudgazing
• looking at fucking everything through a high mag loupe
• tarot divination
• contact juggling
• kefir making
• key duplication by hand
• sleeping
• hiking
• floccinaucinihilipilification
• origami
• talking to nearby friendly looking strangers
• polishing
• cleaning
• caligraphy
• drugless hallucination
• soapbox public speaking
• zen gardening
• guerilla gardening
• pitch ear training
• 'easter egg' hiding
• local botanical/ecological studies
• flint knapping
• home/interior design (as long as you don't actually buy anything)
• knolling
• marble running
• solo RPGs like 'Alone Among The Stars' (okay this one wasn't technically off the top of my head. I couldn't remember the name, so I looked it up.)

• Building your own transit lines on a map. I do it on the website called metrodreamin sometimes. Very fun!
• Writing policy docs/bylaws/rules for literally anything. Can be a country, a city, a coop, some fictional entity, anything! Completely free. When I actually write stuff, it helps me understand my own beliefs and opinions much more clearly. Bad opinions become a lot easier to spot when you write them out. Stretching these "rules" to their logical extremes is so fun too! Helps you understand holes in your opinions/limitations. I remember writing down my ethical framework. So fun!
• Programming. It's free. You can play around n do whatever.
• Reading porn. Written porn vs audio-visual porn is such a massive massive difference. Written porn often has something that audio visual porn doesn't - emotions. Also, the setup for written stories is so much cooler than audio visual stuff.

Hiking/going for walks, sketching, reading (public domain books are free at project gutenberg, libraries are free), watching shows/movies (again, libraries offer access to this locally and through apps like Hoopla, Kanopy, etc. and there's free streaming off Pluto.tv, Shout.tv, Tubi, etc), music (again, libraries or free streaming), body weight exercises and cardio don't require a gym.

Might add more later...

Check out your local library! They have books of course, which can open up all sorts of new hobbies, but modern libraries also can have computers, free classes, workshop and maker spaces, tool borrowing, and sometimes even video games and the like. My local one even has free tickets to museums and the zoo!

If you want something free/cheap as hell, take up drawing. You don't need fancy art supplies, just a pencil and paper. Look up proper drawing classes and books and get awesome at sketches!

I started learning the drums before I got My drums. You can learn the theory and practice beats on the objects around you. That's the cool thing about drumming: everything in the universe is technically a drum!

macramé was mentioned but I want to mention that if you see it you will think maybe it is hard but its literally doing the knot where you take two strings and loop them around each other so pulling the string just makes it tigheter. Also you can make a sling from it sized to fit something like a tennis ball or any other ball you have around and then you can take it to a tennis court (parks around me tend to have them) and then practice slinging it. Big plus to do with a dog.

Pottery. Clay is free. Water comes from the sky. If you have like a bucket or something, you're set. You can fire it in an oven you make yourself. Out of clay. For free. Clay is great. Highly recommended. Ask your physician if clay is right for you.

Also, be careful where you source your clay from. You don't want to get Lynks disease.

gooning

Hiking can be nearly free especially on beginner trails that don’t require special equipment

Writing is something I hated in school but as I’ve gotten older it can be fun to kinda play god with peoples lives.

Cooking isn’t free but could actually save you money if you eat out a lot.

Chess. You can try Lichess, a free (and open source) website/app to play chess. There's countless of videos and tutorials on the internet about chess.

If you have a computer, you can learn to write code. The market for programming is in shambles, but that doesn't mean it can't be fun. You can do all sorts of things like make a game, build a personal website, make a custom app, make art, and more

TTRPGs like GURPS or OpenD6 for free group activities. All you need are pencil/paper/notes app and 3 6-sided dice, and you can roll them with an app or on plenty of webapps (dddice.com is a good one for shared gaming). A lot more to learn than playing cards or board games, but much more fun than a typical game night, something the group can talk about all week between sessions.

I looove to do Geocaching. You combine hiking with Geocaching and it's a game changer