My friend Ari OH2BSF built his version using Raspberry Pi instead of a laptop. Othervise the setup is the same than described in the previous posts, soundmodem as TNC and xastir as APRS client.
Hugo XE1BEP has built a similar system, and he has also written an excellent document how to turn a Raspberry Pi into an iGate using xastir and soundmodem. His version includes the instructions how to connect a serial GPS into the system. Here is the link to his document: