Chrome OS (on Chromebooks) and CloudReady (x86 PC) have native support for L2TP/IPsec VPN. To setup a L2TP/IPsec VPN connection, do the following:

1. Open the Settings in lower-right menu
2. +Add Connection > OpenVPN / L2TP
3. Use the following settings

Server hostname: the server address/location you want to connect to, from the list at https://vpn.ac/status such as nl3.vpn.ac (use the alternative addresses for users in China if you connect from China).
Service name: a short description, such as VPN.AC L2TP NL
Provider type: L2TP/IPsec + pre-shared key
Pre-shared key: vpnacshared#
Server CA certificate: Default
User certificate: None installed
Username: your VPN username
Password: your VPN password
Group name: leave blank

Check Save identity and password if you want to save your credentials and click Connect.
You can find the connection in the menu for quick connect/disconnect.