Today I needed to draw a number of sequence diagrams and since I do not have a program installed for this I decided to look online. My search was successful and I was very happy to find websequencediagrams.com. What sets this tool apart from others is that you do not draw the sequence diagram but you write it. Just up my alley as a developer. Using easy syntax like the below you can quickly stitch a diagram together.
Alice->Bob: Go do it! Bob->Alice: Okay! Bob->Charles: Help me please! Charles->Bob: Done! Bob->Alice: Done!The above would yield this diagram.
There's a number of styles to choose between such as napkin, plain UML etc.
There are probably other such tools but this fit the profile and use case for me.