SMStoXMPP is a lightweight PHP-based SMS to XMPP bi-directional gateway application which receives messages from an SMS gateway device/application and relays them to the target user via XMPP. Replies to the user can be made via XMPP, which then delivers the message back to the SMS gateway.
SD SMS Master is an SMS-sending server. The Web server (master) contains the SMS Master itself. Clients (users) connect to the master and create orders. Orders contain a text to send and a list of numbers to send to. The master then connects to remote machines (slaves) and distributes the order numbers (+text) to all enabled phones on the slaves. The communication is one-way; incoming SMSes are not read.
Ozeki NG SMS Gateway sends and receives SMS, MMS, email, and voice messages via GSM modem connections or directly over the Internet (SMPP, UCP, CIMD2) to/from mobile phones. It is useful for SMS services like SMS notifications, two-way SMS systems, automated SMS services, SMS paging, SMS games, billing systems, email-to-SMS forwarding, premium rated SMS services, etc. It supports various APIs.
eSMSd is a simple daemon for connecting a Gnokii-handled mobile phone with SQL database into a SMS gateway. It bears great simplicity, and is therefore suitable for custom projects and smaller businesses, but is still powerful enough to handle larger loads. The project is intended as a replacement for Gnokii's SMSd, but is much simpler (therefore great for hacking, learning, and SMS magic) and also a little more portable (SMSd tends to crash on AMD-64).