I have an HP MicroServer N40L that I bought several years ago, and it's almost a doorstop now. Its CPU (dual-core 1.5 GHz AMD Turion II Neo) is slow and doesn't support AES-NI. It maxes out at 8 GB of RAM (16 GB of RAM if the stars align and it likes the RAM you bought). It has one GigE port, and SATA ports are limited to 3 Gbps (SATA II). Expansion is limited to an eSATA port, USB 2.0 ports, a low-profile PCIe 2.0 x1 slot, and a low-profile PCIe 2.0 x16 slot.

It's okay as a NAS that mostly sits idle and occasionally serves up unencrypted data at GigE speeds or less. For more demanding tasks, it's woefully underpowered.

I have one of those. Finding the RAM is pretty easy, I'm running 16GiB of ECC RAM. Cheap, too, because DDR2 if I remember. You can put a NIC in the PCIe slot. The SATA ports are fine for spinning disks. You can use the drive bay which is also SATA.

Of course it always depends on the use-case, but for most people at home it's sufficient. I use it as a Minecraft and media server.

That'd be adequate for a simple nas (samba/dav) and maybe running a 24/7 torrent client with a simple web interface but that's it, yeah.

Still, a box is a box :P

Underpowered? With that much hardware I could run 32 Q3 and UT99 servers at once without blinking.

Yes! I'm dreading the day when my N36L dies. So far I've only had to replace the PSU fan. And it's weird that no other manufacturer has anything like it. Compact case, not too noisy, houses 4 disks, runs FreeNAS.

Supermicro has a number of servers with a similar form factor.

The closest to a classic HP Microserver is the SuperServer 5028A-TN4, although that one uses the Atom chips that have been recalled.

There's also the much more powerful SuperServer 5028D-TN4T.

They also have a bunch of older models whose names escape me, but can be found by searching for "supermicro mini tower".

That looks promising, thanks for the tip!