Only tested on Digital Ocean Debian 7 x64/x32 and Debian 8 x64.
Well I guess it would work on Ubuntu, LOL.
The l2tp VPN supports IKEv1, IKEv2, etc.
So iOS, Mac OS, Windows and Android are all supported, esp the 1% Windows Phone users :)
About how to use it, please check the ref3 part 4.