Most people running something small do not need accounting software. They need somewhere to write down every payment in and out, against a category that means something, so that at the end of the year the total is a fact rather than an afternoon with a bank statement and a highlighter. This is that, in a page, with the arithmetic done and the summary an accountant will actually accept.
It is a cash book, which is what most people actually need. Money in, money out, a date, a category and who it was. That is the record a self-employed person, a club treasurer or a small charity is required to keep, and it is the record an accountant will work from. Anything more elaborate is usually somebody selling a subscription for a feature that will be used twice.
The categories are yours and they should be few. A category is only useful if the same thing always goes in the same one, which means having a dozen rather than forty. The list offers whatever you have used before, so the second entry of a kind is a keystroke rather than a decision, and a typo shows up as a category with one thing in it.
It adds up, and it shows the working. Every total on the page is worked out from the entries in front of you, and the summary names each category, the number of entries in it and what they come to. Nothing here is derived from anything you cannot see, which is the property that makes a disagreement about a number resolvable.
Not accounting advice, and not a tax return. Whether something is deductible, when income falls, how a scheme applies to you: those are questions for somebody who knows your situation. What this gives them is a clean, complete list of what actually happened, which is the part that costs money when it is missing.
It stays on this machine. Your income is nobody's business, and a page holding it that also talks to a server would be a strange thing to trust. There is no account, no subscription and no server here. Export the JSON regularly and keep it somewhere: a browser is a place to work, not a place to store the only copy of anything.
No, it is single-entry: one line per payment, in or out. That is what cash accounting looks like and it is what most small operations are required to keep. If you need debits and credits against a chart of accounts, you need an accountant and their software, and this will still be a useful way to hand them the year.
Use a category or the reference field to say which account a payment went through, and filter on it. Separate ledgers in separate browsers would be worse, and a second balance column would make the page harder to use for the many people who have one account.
Record what actually left or arrived in the account, which is the gross figure, and put the tax element in the reference if you need it. Working out what is reclaimable is the job of whoever prepares the return, and they need the real numbers rather than your arithmetic.
Yes, which is true of anything stored in a browser. Export the JSON now and again and keep it with your other records. If a folder is connected, a CSV of everything is written to it as you work, so there is already a copy outside the browser.
Not at the same time, and nothing here pretends otherwise. Pass the JSON file between you, or keep it in a shared folder and load it before working. Anything cleverer needs a server, and a server is the thing this does not have.