I build my own stuff.
Mailchimp for my Daily Inspiration mailing list? Nope. I've got a Linux server with Sendy using Amazon SES for mailing list distribution, with a signup form via Carrd.co. Dirt cheap compared to alternatives. It's fronted by AAPanel since it's Apache.
Mastodon? I've got my own instance, so I'm @jimcarroll on futurist.info. That's on a small scale Vultr server, about $10 a month.
My Web site? A self hosted Linux server with Wordpress front ended by CloudPanel for server management since it's Nginx. A Hetzner box.
My 'other' Daily Inspiration site to replace Substack? it's a Ghost server on a Linux cloud somewhere, also fronted by CloudPanel.
And don't even get me started on my 'server farm' that I've got downstairs in my home with some old Macs running Linux, a couple of Zimablade's, a few PC Linux boxes and a 2009 Mac Pro tower.
How are they used? A good example - cheap webcams at home and the chalet? I grab the feed via RTSP into Sighthound and SecuritySpy hosted on said machines so I don't have to pay a company for my webcam stuff out in the cloud.
I could go on.
Build your own stuff.
It's therapeutic.