There's a Roth 401k and a Roth IRA. The Roth 401k has a combined contribution limit with other 401ks ($23k). Like you said, it gets taxed in the front end and not the back, which is likely only going to be better for people withdrawing $100k a year or something from it.
The Roth IRA is totally separate. It carries the Roth name because it gets taxed the same on the back end, which makes it confusing, but it's contribution limits are entirely separate from any 401k stuff. $7k annually, with limitations on upper incomes being eligible. It is run by financial institutions, not plan administrators like 401ks. This is the one I regret not having funded until now. The advantage with this one is your gains grow tax free, no capital gains, no income taxes on dividends, interest, etc. It is obviously preferable to a private account, and should be funded before those.