What Are Less Computationally Demanding Alternatives to the Viterbi Decoder?
An straightforward alternative to a Viterbi decoder for decoding convolutional codes is a Sequential Decoder.   The algorithm is simpler, but the performance isn't as good.   For example, the common constraint lengths for systems using Viterbi decoding are typically k = 7 or k = 9.  A system decoded with a sequential decoder typically has a constraint length in the thirties or so.   The complexity of a Viterbi decoder would be prohibitive at such a long constraint length, and the performance of a Sequential Decoder is very poor with the short constraint lengths used with a Viterbi decoder.

Another alternative would be to use an APP or MAP decoder, but those are more complex than a Viterbi decoder (since they're essentially two Viterbi decoders running together in opposite directions).  But if you just want to say you're not using a "Viterbi" decoder that might qualify.