As far as the coast goes, it was largely controlled by Muslim Sultanates, generally founded by Arab or Persian traders, which developed into the Swahili culture.

One was the Kilwa Sultanate (centred on Kilwa island, modern day Tanzania), another was the Sultanate of Mozambique island, a third was the Angoche Sultanate south of the Mozambique island sultanate, supposedly founded in the 1490s by refugees from the Kilwa Sultanate.

There was also the sultanate at Sofala (again in present day Mozambique, south of the Angoche sultanate), which while it had been under the control of the Kilwa sultanata, had some kind of tributary status with the African Kingdom of Mutupa, allowing them to trade there.

Mutupa was a Shona empire which stretched from the Zambezi and Limpopo to the Indian ocean. Other than the Kingdom of Mutupa, I'm not aware of the political situation of other inland African Kingdoms or tribes.

It really depends on what part of South-East Africa you're referring to.

The interior of the area (Zimbabwe sort of area) was home to a succession of fairly substantial kingdoms / empires, the most well-known of which is the Kingdom of Zimbabwe. These empires grew rich off resource trade to the coast, particularly gold, and built fairly substantial cities. As well as Zimbabwe itself, there was the Kingdom of Mapungubwe before it, and Mutapa and the Rozwi after it (who were the empires in the region when Portugal arrived.)

Most of the trade these empires carried out was with the Swahili city states, which were mainly around sort of Tanzania through Somalia but did extend into northern Mozambique and Madagascar. These were established primarily by Arab traders, but as Indian ocean trade increased it became much more of its own thing instead of remaining linked with the Arab states. On the whole, these were mainly just city states instead of an empire which controlled the whole coast, but they did have a fair bit of influence in the region. The Swahili states were a popular source of origin for early European explorers in the continent, as the frequent expeditions into the interior by these states to capture slaves allowed a much easier path in than say the Nile or Congo rivers.

There were a fair few other kingdoms in the area - Madagascar was largely under the control of the Merina, while the Zambezi floodplains were home to the Lozi. Southern Africa was home to a whole host of different tribal groups, though again these didn't necessarily operate in isolation. There's quite a bit of history in the area, but much of it is still not that well known for various reasons.

Sorry this isn't quite as detailed as I'd imagine you'd have liked, I ran out of time. Let me know if you want me to give some sources and I can put them up later on when I get home

I wouldn't be able to answer the question either way, unfortunately, but I have a counter-question for you:

What's the difference? To me a kingdom and a tribe are more or less the same, only one is used in a kind of derogatory sense about what one might consider 'less civilized'