The Lightweight and Efficient Application Protocol is a set of protocols designed from the ground up to support wireless IP applications. Work on these protocols has continued as a response and solution to the problems that the current crop of closed solution platforms (WAP, bluetooth, etc.) present to the entire wireless industry. These protocols have been published as an open standard in RFC format much like other de facto Internet protocols to promote their adoption. The current wireless killer app identified by the LEAP forum is Short Messaging Service (SMS), and they have endeavored to meet the specific requirements of this application and have completed the protocol suite up to a working implementation.
Work on the protocols that form LEAP began in 1994 in McCaw Cellular's wireless research and development group. In 1996 McCaw Cellular brought in an outside consulting firm, Neda Communications, who worked under contract to develop an efficient wireless message transport and delivery system. In 1997 AT&T acquired McCaw and abandoned work on the project, but Neda Communications had secured the proper rights to continue the development of the wireless protocols. LEAP was eventually completed by Neda and published as RFCs. To this day the primary company behind the work on LEAP is Neda but it does remain an open standard, freely distributed and open to peer review.
ESRO is detailed in RFC 2188: AT&T/Neda's Efficient Short Remote Operations (ESRO) Protocol Specification Version 1.2.
"When TCP is too much and UDP too little" (Banan 1995), Efficient Short Remote Operations provides reliable connectionless remote operation services, and runs on top of UDP. ESRO takes care of segmentation and re-assembly, concatenation and separation as well as multiplexing. Obviously LEAP is IP-based because it runs over top of UDP which in turn runs over top of IP.
Please see Efficient Short Remote Operations for more information.
EMSD is published in RFC 2524: Neda's Efficient Mail Submission and Delivery (EMSD) Protocol Specification Version 1.3.
Efficient Mail Submission and Delivery is a message delivery protocol that provides the same kind of services as SMTP for normal e-mail. It runs on top of ESRO as SMTP runs on TCP.
EMSD aims to combine the best parts of traditional paging and email. It is an elegant system combining the structure and interoperability of e-mail with the mobility and "Push"-model delivery of paging. Also, EMSD is optimized for the wireless environment: it's shown to be about 5 times more efficient than SMTP in both number of packets transmitted and number of bytes.
Please see Efficient Mail Submission and Delivery for more information.
LEAP vs WAP
For more information, and a direct comparison of LEAP and WAP check out my LEAP vs WAP node.