MscGen
MscGen is a small program that converts Message Sequence Chart descriptions to images. Message Sequence Charts (MSCs) are a way of representing entities and interactions over some time period and are often used in combination with SDL. MSCs are popular in Telecoms to specify how protocols operate although MSCs need not be complicated to create or use. Mscgen aims to provide a simple text language that is clear to create, edit and understand, which can also be transformed into common image formats for display or printing.