so who else makes this HTC555 Digital 555 Timer

Don't know, but it's very different from the classic Signetics 555, and if I'd been them I would not have called it 555, especially since it's in the same package.

I think (without looking up all the details) that not only is this not a 555 derivative, it is actually a programmed PIC microcontroller (or maybe AVR). The frequency accuracy, power pins, and general frequency range are what I'd expect...

So to answer your question, I could make one myself in a couple of hours or less. A single-frequency version, much quicker than that.

Still, it's a handy thing to have available for people who don't want to program a microcontroller for every simple project.

I should add...

When I say I could make one, that doesn't mean you shouldn't buy theirs. If I knew how to use a metal lathe (which I don't), I'd be able to make my own nuts and bolts. But that doesn't mean I'd never buy them at the hardware store!

I rather like the Hightechips approach to packaging preprogrammed microcontrollers as solutions to analog electronics problems.

"Our approach towards product development allows us to introduce new products rapidly and effectively. We have found the secret of how to do this without affecting the quality of our end product."

Their secret being writing a bit of code and burning it into 35 cent Microchip PIC12F50x.

Bit dishonest and pointless of them to pretend they are not doing this.