The best replacement for c99 is c89.

The best alternatives to c99 are rated as following:
★★★★★  c89
★★★  ansi c
★★★  gnu99
★★  jack herer
★★  r57
★  c90
★  kali mist
★  c11
  c98

Your alternative for c99 is not listed? Suggest!
Speaking about c99, one probably shouldn't forget about gcc.

Other search terms related to c99 and their ratings are:
★★★★★ gcc
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c99
c89
ansi c