RSI
The ratio of upward to downward strength over 14 candles, scaled from 0 to 100. The core uses the levels 30 and 70: below 30 is oversold, a reason to expect a bounce; above 70 is overbought.
Important: in a trend RSI can stay above 70 for weeks. That is exactly why the RSI reading counts in the range regime, while in a trend a bounce from 50 is used instead.
RSI(2)
The same computation over two candles — it reacts almost instantly. It looks for very short oversold readings inside a range: price jerked down over a couple of candles, and statistically it more often comes back.
Stochastic
Compares the close with the range of the last 14 candles: where exactly in that range price closed. The classic zones are below 20 and above 80. StochRSI is the same thing applied to RSI itself: it reacts more sharply than the plain stochastic.
CCI
The deviation of price from its average, normalised by dispersion. The levels are ±100: moving beyond them means price has gone noticeably further than usual. Counted in a range as a reversal factor.
What oscillators cannot do
They do not distinguish "overbought and about to turn" from "overbought and still rising". A single oscillator is an opinion, not a signal; which is why the service requires several factors to agree (the minimum number of cores).