I plan to be in South Africa for a year to work on a personal project. Someone told me that since I won't be there as a tourist, I will be liable for tax on my worldwide assets - is that true? I'll be eating into savings as it is, so if that's the case, I'm not coming!
Whoever told you that has absolutely no idea what they're talking about!
Depending on your nationality, you can enter South Africa for up to three months without a visa or on a tourist visa. Thereafter you'll need some kind of temporary residence visa. Have a look at Visas for South Africa for more info.
You need to be here a total of 183 days in one tax year to be liable for tax - but it will only be on your income generated within South Africa. You need to be here for five years to be considered a resident, at which point yes, you will be liable for tax on your worldwide income.
To read more about this, take a look at Tax in South Africa and Banking in South Africa.