The ICL7660A is a
charge pump controller, many manufacturers have similar parts with various capabilities as you've seen. Be aware that some of them have trouble starting under load and so some applications require an esternal schottky diode across the output.
A charge pump is fundamentally a square wave generator plus a couple of diodes, so if you don't need much current, you can create a charge pump from a spare PWM output from an MCU plus a couple of external diodes and caps. This is handy for LCD bias voltage, for instance. The drive strength of the MCU's IO pins will be a limiting factor in the amount of current such a charge pump can provide, but you could add a couple of transistors to improve this if you wanted. You could also use a 555, as mentioned, and you can even daisy chain pump stages to create higher, lower, or bipolar voltage output options.
More generally, if you need more current, you can configure a standard buck converter as an inverter--what would normally be the output node gets tied to ground, and what would normally be ground becomes the negative output. Note that in this configuration the converter sees the full potential between the positive input and the negative output as its supply voltage, so watch the switch voltage rating, and any control/status signals will need to be referenced to the negative output rather than ground.