You can safely use gets on trusted input. For example, your program might create a pipe or socketpair to communicate between the processes that result from a call to fork. The stdout of one process feeds into the stdout of the other process.

Unless you have an insane gets implementation that writes the bytes backwards, you can also safely use it on untrusted input. Simply place a guard page at the end of the buffer. You can do the call from a forked child that you let die, taking notice of the problem in the parent. On systems without threading (because of locks in libc) you can do a longjmp to recover.