Is there a website that offers free online skills assessments?

What you are seeking is called professional development. The professional development "industry" is far to profitable to provide resources for free.

With that said, I would encourage you to visit a local community college or university in your area. Often times there are departments who offer the kind of courses you are looking for. They either offer them on line as certificate courses, or in face to face sessions. The cost of such courses has a good price range to it.

I would research continuing education programs on google in the city or region you live in. This might provide some leads.

If you are trying to sharpen or enhance your skills, sadly, the only way to get there is to earn it and pay for it.

I hope this helps!

I believe that www.brainbench.com offers skills assessments though I also believe they charge for them.

Maybe computertraining.com

try www.tickle.com not sure if ull get exactly what u want but its worth a try