The Alamo. A giant convention center. And miles of suburban housing in all directions. For decades, these were the hallmarks of downtown San Antonio.

Now, some deep-pocketed developers are aiming to turn San Antonio into a city better known for hip restaurants, a thriving tech scene and a booming downtown property market. Since 2011, 2,900 housing units have been built or are currently in planning or construction—about five times the number built in the previous decade, said Lori Houston, San Antonio's Center City Development and Operations Department director.

In northwest downtown, workers are at work renovating a 120,000-square-foot, century-old former department store into the new home for Geekdom, a communal workspace for tech professionals, which has 800 members. The building will eventually have a cafe, a rooftop bar, and other amenities "that the geeks want," said Randy Smith. Mr. Smith is the president of Weston Urban, a real-estate development company founded in 2012 that aims to "create the ecosystem for tech entrepreneurialism" in San Antonio, Mr. Smith said.

Mr. Smith co-founded Weston Urban with Graham Weston, a native of San Antonio who is the chairman and chief executive of Rackspace, a cloud-computing company valued at $4.5 billion. Over the next five years, Weston Urban plans to develop a downtown district using four surface lots the group bought last year, along with three buildings it already owns, and by buying other properties. The plan includes 1,000 rental apartments plus restaurants, shops and other businesses designed to create a lively downtown.

Public infrastructure projects under way downtown include a $325 million expansion of the convention center, along with a $30 million improvement in Hemisfair Park, where the plan is to eventually build housing, cafes and playgrounds. There's a $280 million streetcar project, of which $210 million has been secured, that would connect 6 miles through downtown with a rail system; and a $125 million plan to create a parklike atmosphere around San Pedro Creek, which runs through downtown. In 2012, voters approved an additional $93.5 million of downtown improvement, said Ms. Houston.