I’ve seen people using buymeacoffee.com. Don’t know much about it. There’s a few others mentioned in the comments here.
What all these platforms do is basically the same. They provide an integration with 1 or more payment processor, like Stripe or PayPal, and build easy-to-use features on top of it, like one-off and recurring payments. One could argue they’re an artifact of Web 2.0 practice, where people host their work on one corporate platform, and then have a micropatronage account on another, because the primary platform doesn’t pay creators, or is fleecing them.
Fair hosting services can have their own integrations and micropatronage functions, and only take a fair commission when processing payments. So arguably, an account on a separate micropatronage platform isn’t really needed. For instance, if you’re using Ghost to host Selecteh (or WP+WooCommerce), these functions are built in.
I can’t find source code, but it seems to be a new project. They may have plans to publish source once they’ve got their feet under them, and the code has stabilized somewhat.
To find source code for a web service, I usually look for a link on the homepage to a code forge (usually GritHub for now), or for one that says something like "developers’, and see if it’s there. Or for any mention of code license(s) on the site. It’s usually considered a selling point, so not too hard to find.
Failing that, especially for new projects, a web search for “[name of project] source code license” usually finds the repo. No results using either of those methods usually means it’s proprietary, at least for now. Although to be sure, you could always contact them and ask.
GNU.org has an essay that explores this question as it relates to network services. In a nutshell; it’s complicated.
I think it makes sense to prefer services that publish full source code, when they’re available. That way if the service operator goes evil, or gets bought out by evil, or there’s some other serious problem with it, the community has the option to set up a new service using the same code. For example, LiberaPay began as a fork of GratiPay, which is now defunct.
But for as long as the overall behaviour of service operators makes them seem like allies, I don’t think proprietary code is a showstopper. Especially when they’re just getting started.
People are often put off applying a free license to their code because they assume it obliges them to run a public issue tracker, review drive-by patches, and so on. All of which increases their workload and the risk of attracting spiky people into their workspaces.
This assumption is wrong. Using free licenses doesn’t oblige developers to make development open to public participation (Android isn’t, for example). But apparently this is what the phrase “Open Source” now implies to many people. So they drag their heels.
I’m not aware of any free license that even requires publishing code. Technically, you just have to make it available to anyone you distribute the software to, if they ask for it.
Obviously publishing code avoids that correspondence work, but you can make your code public without making your project tools accessible to anyone outside your team. Or publish it on a static site, that gets updated every time the code in a private repo changes.
So I encourage anyone running an ethical web service to choose a license, and publish their code. For transparency and accountability, and to put people’s mind at rest.