Mainstream Group Holdings Limited provides fund administration and custodian services for the financial services industry in the Asia Pacific, Americas, and Europe. Its services include investment administration and fund, fund accounting, unit registry, middle office, distressed assets administration, and corporate services to fund managers and listed companies. The company also provides superannuation services comprising member administration, unit pricing, and accounting services to industry funds, corporate superannuation funds, and retail superannuation master trusts, as well as manages accumulation funds, defined benefit funds, hybrid funds, account based pensions and transition to retirement pensions, existing fund takeover, mapping of member data between systems, communication to members, new fund establishment, design consultation, product disclosure statement design and production, and communications program. In addition, it offers registry services, such as listing, transaction processing, and reporting and correspondence services to exchange-traded products. The company was formerly known as MainstreamBPO Limited and changed its name to Mainstream Group Holdings Limited in September 2017. The company was founded in 2006 and is based in Sydney, Australia. As of October 18, 2021, Mainstream Group Holdings Limited operates as a subsidiary of Apex Group Ltd..