Osmocom.org - Community based Open Source Mobile Communications For decades, there is a sheer unlimited number of readily available Free / Open Source Software (FOSS) projects related to TCP/IP/Ethernet networks. On the contrary, until 2009, there was no FOSS in the field of mobile communications protocols like GSM and UMTS at all. Projects like OpenBSC and OpenBTS have changed this ever since. Osmocom.org is a community-based umbrella project containing implementations for various network elements of GSM/GPRS/EDGE networks, including MS, BTS, BSC (OpenBSC), MGW, STP, SGSN, GGSN, etc. Furthermore, it also contains software for GMR (ETSI Geo Mobile Radio, used by Thuraya), as well as TETRA, DECT and APCO25. This lecture will give an overview about the different osmocom.org projects, their applications and the motivation of the people who implemented the software.