slingshotsms is a minimal SMS server which builds on the work of pygsm, an excellent Python library for dealing with AT-compatible modems. What this means is that slingshotsms is compatible with Mac, Windows, and Linux, and can interface with a wide range of GSM modems and cell phones - including many sub-$200 field-ready modems like the one we use for testing.. The software itself needs minimal configuration and is small enough to run on a USB stick.
Download and try out slingshotsms at GitHub
You can also download a cross-platform binary package suitable for USB sticks without any installation.