Other system limits

These limits apply to the entire system:

A maximum of 4095 active at any time, except on versions of ARM before v6, where the limit is 63 processes.

On ARM platforms, the limit is actually on the number of separate address spaces; you could have more processes if they happen to be sharing an address space because of vfork(), but that's very unusual.

Prefix space (resource-manager attaches, etc.)
Limited by memory.
Sessions and process groups
4095 (since you need at least one process per session or group).
Physical address space
No limits, except those imposed by the hardware; see the documentation for the chip you're using.

These limits apply to each process: