After playing with Fun House (and using a simple clock screensaver made in the great Quartz Composer), I found another app that made it worth installing the Developer Tools. Using the AU Lab utility, you can (amongst other things) easily send a sound over a local network. One of the applications could be using an old iBook as a listening device for baby sitting:
- On the transmitting side, turn down volume to avoid feedback, launch AU Lab (in /Developer -> Applications -> Audio), select the proper Input Source from the pop-up menu, and then click the Add Input button on the Inputs tab when creating new document. Click OK to create the new document.
- Under Effects in the Audio Device side of the new window that opens, click the pop-up and choose AUNetSend. Decide data format (AAC 128 Kbps works) and enter a Bonjour name.
- On the receiving side, launch AU Lab and make new document, this time without inputs. Then, in Edit menu, choose Add Audio Unit Generator. Choose AUNetReceive and click OK. In the new Properties window, select the desired Bonjour name and click button Select Host.
PS: When using only the built-in mic, make sure you choose Mono on all dialogs and palettes, to save network load.
[robg adds: This hint covered another use for AU Lab. I have not tested this one...]

