Santa Barbara-based Yardi, which develops real estate and property management software, has acquired another firm, saying Thursday tht it has acquired the Multifamily Services Group (MSG) unit of ista North America. Financial terms of the acquisition were not disclosed. Yardi said the ista's Multifamily Services Group provides energy and water metering, billing and management services, serving more than 700,000 apartment units. The unit has employees in Alpharetta, Ga., Jacksonville, Fla., and San Diego, which will add about 200 employees to Yardi. Yardi has been in an aggressive acquisition mode in the last few months, having purchase Lead Management Solutions in April, ALMSA Corporation in January, and Multifamily Insurance Group in August.