Webflow is a very flexible tool for creating a portfolio site. It is based on CSS and to modify one of their templates – or to create one from scratch – you will need to study your CSS.
Webflow offers a number of portfolio templates – free and otherwise.
The free Smith portfolio template was deemed easiest to use by a recent class.
Other Webflow portfolios to try out are Portico, Craig Roush, and Profolio. At the time of this writing these are all under $50. One student reported that adjusting the Profolio template caused problems.
Squarespace offers a lot of portfolio templates as does Wix. Neither will be as flexible as Webflow but may be easier to work with.
Editor X is a more advanced tool from the makers of Wix that competes with Webflow.
UXFolio is a portfolio tool popular in Europe that looks to have great capabilities.