Sure. google ketlaer & sourceforge, its old -ish but I added on to that a mythfrontend. It runs on the asus oplay, segate fat+, patriot box office, briteview cinema tube, ... (these are the players I use). You can play back recordings from your backend, with comm-skipping (needs some TLC), no livetv and playback of currently recording programs is an issue (stuttering). I may be able to fix that in 025 with http streaming. You can view the epg guide and schedule/modify recordings. It will playback sd,hd, mpeg2 and h.264 recorded via a hd-pvr. I can share my source code modifications. As this builds on some very clever hacking its not perfect - in particular the osd is quite crude. The guy who did all that work sesm to have vanished, But it is definitely usable as a silent cheap front end - doesn't seem to crash. I typically bought these boxes for ~$50 and they can probably be found more cheaply now.
Is there a good reason to pick a specific one over the other? Does any one seem more capable than others, or easier to work with? Do any/all of them work with a Harmony remote? (I actually have an O!Play for the Honda Pilot w/Entertainment System. Load up a 320GB portable drive with hours and hours of shows/movies and give it to the kids. Makes the drive from Colorado to Indiana a bit more tolerable).