[1_player]

StrongSwan is a real powerhorse, even though a bit of a b*tch to configure to work out-of-the-box on most platforms. The documentation is scarce and the wiki was a bit out of date IIRC.

I'm using it on my VPS, with my Mac as a client to bypass the UK big brother, and on Android to bypass tethering blocks (in conjunction with the Tether app)

[Florin_Andrei]

For site-to-site PSK tunnels it's really trivial to setup. Just install the package, copy/paste a config from the docs, add the PSK on both sides, and start the service. Wham, bam, thank you ma'am, you're done.

[nikanj]

And if it doesn't work, there's plenty of forum posts available listing the same symptoms. No solutions usually, but at least you're not suffering alone!