U.S citizens can easily purchase Vanguard etfs to invest in indexed stocks or bonds. Are there any similar options for EU citizens, and which?
Regarding your question in your comment on if you could buy Austrian ETFs as a Spanish citizen: If your broker offers Austrian ETFs you can buy them as well. I do not believe that there would be any legal restrictions.
For a good international broker, which would allow you to buy these ETFs I would recommend looking at Interactive Brokers.com
There are hundreds if not thousands of index funds and ETFs in the EU, far too many to enumerate here. It's worth pointing out that Vanguard themselves operate in the UK. The minimum investment if you go direct to Vanguard is £100,000, but you can make smaller investments through a number of fund platforms.
I have only found solution for UK residents so far, see the article on This Is Money: