The Osmocom open GSM network stack: osmo-trx drives the SDR, osmo-bts is the base station, with osmo-bsc / osmo-msc / osmo-hlr forming the core. Together they stand up a full 2G cell on an SDR, the reference open platform for a test/rogue BTS and active IMSI-catcher research. Actively maintained.
Lifecycle not assessed: nobody has checked yet whether this tool is still maintained, sold or working. Check the project's own page before relying on it.