Things like "2M2B", tertiary-Amyl alcohol.
The downsides tend to be foul taste and massive potency - much over 15ml can kill someone. It doesn't undergo metabolism to aldehyde so the traditional hangover doesn't happen, and the duration can be much longer.
There are others. I'm not vouching for the safety of any of them (even ethanol!), for the record, and have not tried 2M2B.