Ask HN: Those making $500+/month on side projects in 2018 – Show and tell
I’m a full time developer but own a gym. By accident! 
I went to take over a building as office space that was a liquidated gym. Signed the lease and the day before we moved in the owner called and said we can’t remove the equipment as it was all put in before the stairs. I asked a lot of questions about why the gym didn’t work, had already seen the equipment in there and did some negotiating on purchasing the kit, knowing I could still convert an area to offices. 
The gyms main failure was due to the cost of staff. So I fully automated everything, door access, lights, aircon, TVs etc etc. Built a membership system. Making it a fully automated unmanned gym!
We then recruited a freelance personal trainer who does all the inductions in return for advertising and doing PT in our facility with no charge. 
2 years in and it’s making £4,000 profit a month with minimal costs. Now looking to buy the building. 
Gym: https://180fitness.co.uk
Me: https://roybarber.com