Although SiFive's page still doesn't say, other sites indicate the 64-bit main U740 CPU (four U74 cores and one "little" S7 core) is clocked at 1.4GHz. There is 2MB of L2 cache and no L3, plus 32MB of flash and 8GB of DDR4 RAM onboard; it doesn't look like there are any slots for more. A single 16x PCIe 3 slot is available for cards, though it also has Gigabit Ethernet, four USB 3.2 ports, an M.2 E-keyed slot (PCIe x1) for wireless connectivity and a MicroUSB console port (presumably some sort of serial console). For your storage options it offers on-board microSD and another M.2 M-keyed slot (PCIe x4) with NVMe support. That's good, since it lacks a BMC-like console, so you'd almost certainly need to install a video card in that single PCIe slot to use it as an effective workstation. Additional devices and creature comforts would have to be attached by USB.
The price on Crowd Supply is a surprisingly reasonable $665 for the bare board; you add your own case, PSU and peripherals. That's a little over half the cost of a Blackbird board and even includes the CPU and RAM (as long as you don't need to upgrade them), plus a 32GB MicroSD card and 3-metre Cat5e cable, though I'd rather forgo these towards the cost of a GPU. Before you go thinking this is a Blackbird-beater, however, remember even the wimpiest Blackbird with the lowliest 4-core POWER9 (like the one I have in the home theatre) would clean the floor with this system and the Blackbird has substantially more options built-in (two PCIe slots, DIMM slots, SATA, USB, audio, HDMI, three network ports and a "classic" DE-9 serial console). While Raptor is still backordered on the Blackbird, the T2 Lites they do have in stock would serve you even better in the CPU and PCIe department, even if the size is a little inconvenient and they don't have all the creature comforts onboard. And as for comparing it with the big T2, well, let's just all have a good laugh and get on with our day. There's a reason they cost more.
The other, more relevant question is how "open" this machine actually is. RISC-V is indisputably an open ISA and always has been, but it's everything else on the board that's the question mark. While SiFive offers the Freedom U SDK to build your own custom Linux distribution, that's not the same as being able to control it from the firmware up like the POWER8 and POWER9. SiFive notably doesn't make any claims about the lowlevel firmware and I don't think it's cynical in this case to assume that they don't provide source or a means to build it; your control of the system therefore starts at U-Boot. Otherwise, why not be up front about it, since everything else in the RISC-V ecosystem is all about openness?
If this is really the RISC-V PC they promised it sounds like a decent system for the money, certainly on par or above the high-end RPis people already try to make workstations out of, and I always encourage anything that weakens the x86 monoculture. For that matter, I'm actually toying with getting one myself for comparison purposes, since right now it looks like the most convenient way of experimenting with RISC-V other than an evaluation board. But also know that you're not getting a system on par with OpenPOWER performance or owner control, at least not in this iteration, and a lot of engineering work and a bit of policy change will have to both occur for that to happen. As of this writing, 113 boards have been backed on CrowdSupply with 16 days to go, and boards are expected to ship January 15, 2021. If you're picking one up or know more, post in the comments.
