I'm Khai Do, an independent developer in Vietnam. This domain hosts what I work on: the pages a shipped app needs, and the private tools that don't need a front door.
Everything here is built and maintained by one person, which is the reason it stays deliberately small.
A subscription and bill tracker for iPhone and iPad. It keeps every renewal, trial and recurring bill in one place, reminds you before a charge, writes renewals to your real calendar, and works out what's worth cancelling — without a bank login, an account, or a server of mine holding anything.
Available now on the App Store
The rest of what runs here is private: internal tools with no public sign-up, sitting behind a login on their own subdomains. They aren't products, they have no marketing pages, and they aren't listed.
support@aquifer.fyi reaches me directly. It's a mailbox that gets read, not a ticket queue — expect a reply within a few days, in English or Vietnamese.