Or Pinephone with a keyboard addon: https://www.pine64.org/2021/08/15/introducing-the-pinenote.

I had an N900- for me one of the main downsides of it was the touchscreen, it was fine but with my colleagues all using the HTC hero it was frustrating to set their devices up for them and see how much nicer the experience was with multitouch.

Very solid device otherwise- i went from an Xperia X1 to the N900.

Another option is https://fxtec.com/ although it doesn't seem to have a second screen on the back.

It's a slider so it doesn't need the back screen.

For those looking for modern PKB phones the Unihertz Titan and the upcoming Titan Pocket are some other good options.

At least that one has a PMOS wiki page: https://wiki.postmarketos.org/wiki/F(x)tec_Pro1_(fxtec-pro1)

It says debian support is "planned" but I wonder what exactly the plan is. Looking around it sounds like a bunch of drivers are missing for that SoC, is the plan to re-implement them? Wait for the community to re-implement them?

N900 was absolutely my favourite out of all phones I owned. It felt like such a power-user device.

Related, the Neo900 project apparently gave up. Does anyone know why?

They had massive organizational problems. At one point years ago I received a series of e-mails asking for permission to move my preorder funds from one org to another. That's when I wrote them off.