Aaron Swartz’s company that merged with Reddit in 2005 was Infogami.
Swartz founded Infogami with Simon Carstensen in 2005 as a web-based publishing and content-management project. The company participated in Y Combinator’s first funding batch, but it struggled to secure additional financing after the program ended.
Y Combinator’s organizers suggested that Infogami merge with Reddit, which had been founded by Steve Huffman and Alexis Ohanian earlier that year. The merger took place in November 2005 and produced a parent company called Not a Bug, Inc.; Swartz became an equal owner and joined the Reddit operation.
The merger is sometimes summarized as Swartz “joining Reddit” or as Reddit acquiring Infogami, but Infogami is the company name the question asks for. Swartz also helped rewrite Reddit’s software using web.py, a Python web framework he had developed. His later status is debated: some accounts call him a Reddit co-founder, while Reddit’s current histories generally distinguish the original founders from the later merger.