Wave is a real double entry accounting system that costs nothing. That is not a marketing claim with an asterisk, the core ledger genuinely is free, funded by payment processing and payroll in the markets where those products are offered.
For a South African business the honest assessment is that free is the entire argument, and it is a weaker argument than it first appears.
What you do not get
There is no South African VAT handling. You can create a 15% sales tax, but there is no VAT201 report and no supply category treatment, so a VAT registered business is doing the return by hand. There are no South African bank feeds, so every statement is a manual import. There is no telephone support on the free product, and the paid support tier is priced in US dollars.
Multi currency is not supported in any useful sense, which rules out anyone invoicing outside the rand.
What you do get
A clean, genuinely double entry general ledger. Unlimited invoices, unlimited users, unlimited transactions. Decent invoice templates. Basic financial statements that an accountant can work from. For a business below the VAT threshold, banking with one account, invoicing in rand only, this is enough, and enough for free is a real proposition.
Who should buy it
Pre revenue startups, side businesses, non profits with tiny budgets, and anyone who needs a legitimate set of books without a monthly cost. Plan to migrate the moment you register for VAT, because at that point Wave stops being free and starts costing you your bookkeeper's time.