For a long time my home server was a dell wyse 3040 that I got for £25 on flea-bay. 1.4ghz quad core x86-64, 2g ddr3 ram, 8gb emmc, <= 5w max load, fanless, runs standard, normal debian like a treat. :) Eventually I got tired of being constantly vigilant about disk space and replaced it with a more traditional desktop, but I still love that little (compute) engine that could (it's still alive as a glorified ereader desktop for the kids -- just enough muscle to run firefox and epub/pdf readers without being capable of distractions).