Until RaspberryPi 3 model B was announced, the RPis were much more usable for education and electronics projects and less useful as full-fledged Mini PC's.
But now all that has changed.

Fact is, Raspberry Pi Foundation sold 8 million RPis from the previous models (3 million just in 2015) and they will certainly grow past the 10 million units milestone by the end of the year.
This means they sell way more Mini PC's that all the other manufacturers we usually talk about on Mini PC DB - most likely Raspberry Pi is the most popular Mini PC currently on the market.
And don't plan to stop here.

RaspberryPi 3 model B Mini PC full specs

• SoC: Broadcom BCM2837
• CPU: 1.2GHz Quad-Core ARM Cortex-A53 (64-Bit CPU)
• GPU: Broadcom VideoCore IV (dual core)
• RAM: 1GB LPDDR2 (900 MHz)
• ROM: via microSD
• OS: Raspbian
• HDMI: 1.4
• LAN: 10/100 Ethernet, 2.4GHz 802.11n Wi-Fi
• USB: 4 X USB 2.0, Micro SD card slot
• Other: Bluetooth 4.1 (Bluetooth Classic and LE), CSI camera port, DSI display port, 3.5mm analogue audio-video jack

RaspberryPi 3 model B Mini PC

RaspberryPi has an entire team behind it (the Raspberry Pi Foundation employs some 60 people) and a huge (and I mean HUGE) community behind it.
So it shouldn't surprise anyone that the software for the tiny PC is very optimized and that there is a variety of operating systems available for it : from the Raspbian OS created specifically for these devices to Ubuntu (Ubuntu Mate, Snappy Ubuntu Core), Risc OS, OSMC, OpenElec or even Windows 10 for IoT.

The Raspberry Pi devices are basically dev boards, so if you plan to use RaspberryPi 3 model B as a Mini PC you'll need to come up with your own power adapter and SD card for storage - even a case.

But worry not, there are dozens of options available from third party manufacturers - the one I like is this one from DX.