Usually, it's the client that buys the developer, such as Bentley Systems buying up companies that specialize in analysis software, or UGS buying up PLM developers.
Yesterday, uber-developer Geometric Software Solutions of India bought up one of its clients in the USA. GSS is better know for the company that writes a lot of the code in SolidWorks, UGS, the developer of eDrawings, and others.
In this case, Teksoft sold a CAM [computer aided manufacturing] software product called CAMWorks, of which GSS was doing the programming work. Or, as the press release puts it, "Teksoft has its own CAMWorks development team in the U.S. and leverages the offshore programming capability of Geometric which acts as an extension of TekSoft's R&D team."
Now GSS has bought Teksoft, which will now also market GSS's desktop software products [not really sure what those are] in the USA.