PrivateNotes is a cross-platform application for note-taking that allows encrypted synchronization of the notes between multiple instances using various methods. Currently, the following interoperable clients are available:

How to set up an OpenWRT router/gateway as an IPsec/L2TP gateway for Andoid and iPhone clients

The only "reasonable" (that is, not counting PPTP due to its known security issues) VPN protocol supported by default on non-rooted / non-jailbroken Android / iPhone phones as clients is the combination of IPsec and L2TP. Most probably, this was chosen due to its out-of-the-box support by newer Windows clients and MacOS/X as well.