My own Windows gaming-optimization product: 53 reversible tweaks in one click, scheduled cleanups, licenses bound to the motherboard, and recurring billing through Stripe.

01 Sales site in Portuguese, English and Spanish, with monthly and yearly plans and the key emailed right after payment.
Every tweak can be undone individually. Touching the registry, services and GPU settings on someone's gaming rig is only acceptable if the way back exists and is visible, so undo was built alongside each optimization rather than bolted on later.
A key is tied to the machine's motherboard. Reinstalling Windows means reactivating with the same key, no support ticket in between. That kills key sharing without punishing the legitimate customer, who is exactly the person reinstalling the OS.
Monthly and yearly plans through Stripe, with coupons, a 14-day guarantee and the key emailed straight after payment. The whole operation runs without manual steps, from checkout to activation.
NTZ PCBooster is my own product, end to end: a Windows desktop app, a sales site, recurring billing and support. It applies 53 gaming-oriented optimizations to Windows, all at once or one by one, and every single one can be reverted.
It currently has 19 active licenses with zero marketing spend. The number is small and I treat it as what it is: proof that the whole loop works on real machines, from checkout to activation, not a traction metric.
Reversible by default. This category has a deservedly bad reputation, because plenty of tools apply destructive changes and leave users stranded. Here every optimization shipped with its way back, which changes the tone of support: the question stops being "what did you break" and becomes "undo that one".
Motherboard-bound licensing. Tying the key to the machine rather than to an account or install killed key resale without adding friction for people who reinstall Windows, a common habit in this audience.
Automated operations. Checkout, coupons, key delivery, 14-day refunds and reactivation after a reinstall all run unattended, which is what makes a low-ticket product viable for one person.
Live and selling, with no acquisition spend so far. That is the next step: the product has been ready well before the channel.