(Reuters) - Banks, exchange operators and other companies are investing billions of dollars to find uses for blockchain, a digital ledger used by cryptocurrencies like bitcoin.

A Reuters review of 33 projects announced over the past four years and interviews with industry executives involved in them shows the technology has yet to deliver on its promise.

Here are six projects, categorized by their status:

NOT ACTIVE

** Deloitte and technology startup SETL announced in 2016 that they had tested a card payment system based on blockchain. SETL said at the time that the service could launch as early as 2017. The system has not launched, SETL President Peter Randall told Reuters.

** An IBM IBM.N and MUFG Bank Ltd project, announced in 2016, to build a blockchain system to manage contracts between the two companies is no longer active, according to the companies.

PRESSING FORWARD

** Australian Securities Exchange ASX.AX Chief Executive Dominic Stevens told Reuters in May that the exchange expects to go live as planned in 2021 with a blockchain-based technology to replace its over 25-year-old equities clearing and settlement system. The project, announced in 2016, is one of the most ambitious of its kind.

** The Depository Trust & Clearing Corporation expects to go live later this year with a blockchain-based trade information warehouse of cleared and bilateral credit derivatives. DTCC said in January 2017 it was working with IBM and startups Axoni and R3 on the project.

LAUNCHED

** Non-profit advisory group American Association of Insurance Services (AAIS) has launched a system built on blockchain technology from IBM to help insurers streamline data reporting. The group generated a small report and one insurer is loading its data onto the blockchain, while others want to get started, said Joan Zerkovich, head of AAIS operations. But the system is a long way from being widely adopted and a handful of states still require that data be sent on paper, Zerkovich said.

** In late 2018 foreign exchange settlement provider CLS said its new blockchain-based payment netting service called CLSNet had gone live with Morgan Stanley MS.N and Goldman Sachs Group Inc GS.N. Since then, three other banks have joined the service, which was built with IBM, and more will be added this year, said Alan Marquard, chief strategy and development officer at CLS.