The website building firm that Casalena started in his dorm room at the University of Maryland has come a long way since 2003. After several pivots, Squarespace offers would-be web content builders all manner of e-commerce tools, from systems for selling goods or booking appointments to designs for great-looking sites, starting at $12 a month. Lately, Casalena has turned to acquisitions to build the business, snapping up startups Acuity Scheduling and Unfold last year.