The ODROID C0 is a SBC simular to the PI however this is a true DIY board as you have to solder on the USB ports as well as other things from a $2 Connector Pack kit. it also doesn't come with on board Wi-Fi or an ethernet port.
I decided to play with this as an experiment being it was a bit more powerful then the Pi 3B+ and it would fit inside a CM15 very nicely.
There are several Linux distributions available for this but I went with the default image available for it.
I added a mini USB Wi-Fi dongle and installed Mochad with Domoticz which perform well with my limited testing thus far. Hardkernel does sell other ODROID versions that come with pre-soldered USB and Ethernet ports and some even more powerful but these have a larger foot print which most likely wouldn't fit the space available in the CM15A.
There are a few draw backs I encountered:
1- this is limited to two USB port One is required for the Wi-fi and one for the CM15A however these are full sized ports so no adaptor is required. I required a USB hub to set this up as I hard wired the CM15 directly to the board using up a USB port.
2- The SD card location. for me this requires opening the CM15 to access it. However on the Plus side you can use a eMMC instead of the SD card which will provide faster read/writes
3-No ethernet port however this can be overcome with a hub or maybe an expansion card (neither will fit in my CM15)
4-Not really a draw back but this uses a barrel plug for the power supply and this is sticks out more then I'd like. I prefer the Mini USB type power port the Pi uses.
Some Positives:
1-this has a Real time clock you just need to connect a battery
2- this has a port to plug in a battery backup which the ODROID charges while plugged into an outlet( though this would be tight to fit in a Cm15 with the ODROID)
3- The Connector Pack Kit (CPK) comes with the option to solder a one or two port Full sized USB jack I used the single port.
4-the CPK comes with a couple of headers to solder in if needed (I never installed any)
5- the board comes with a special spot to solder in a IR sensor which the USB kit comes with (I will add this at some point )
6- this has a power switch on the board and if battery backup is install still allows it to be charged if switched off
Time will tell how this performs compared to a Pi 3B+ but for X10 and my HA setup this should suit my off grid requirements nicely.
I'm not fully committed to any particular X10 software as yet however I may load this up with HomeGenie as that's what is on the PIs.