I read that the GPS-ILS app mentioned in this thread was discontinued in 2015.
There is however this one. Appstore. I don’t know if it is the same one. The coder has this slightly odd website.
It is IOS only.
As I see it, this app, or any of its brethren, are just good to eventually amuse the armchair pilot…
The app could be enough if one looking to land in VMC? better than visual navigation with 1.5km & 500ft ceilings (FYI, it’s hardcore weather if you have never been there) but I won’t push my luck even if it’s part of PPL privileges 
if one is looking for 550m/200ft, I think an autopilot coupled “proper” ILS is the best we have 
I have not used this app, so I can’t opine on it but I have extensively flown “SkyDemon 3D HSI+GS IAP” and “ForeFlight Synt-Vision”, they work OK as long as one is looking to get down to 3km & 600ft agl if I have to…I also tested few times while flying non-gyro approach at RAF Wittering with everything else crossed with a “post-it”, I would say “toy ILS” & “non-gyro” would be ok if the runway is very long I flew on a sunny day
As always, for any backup one has to try it backup in actual conditions: themselves in their aircraft in their airports & terrains…to see if it’s fits their style (I would have no issues flying DIY-ILS in my home-base in Essex but west of Paris it’s likely to get me killed, unless they remove two construction cranes away from my final)
