Sequences is a lightweight and quick DNA sequence manipulation tool.
A very common task for anyone involved in genetics is the manipulation of DNA or RNA sequences. I need to find the reverse compliment of sequences all the time, and I've been getting increasingly frustrated with the lack of a simple, robust tool to do that - most require strictly formatted sequences, use Java applets which take ages to load, and are generally faffy.
It does a couple of cool things, such as remembering your settings using HTML5 local storage, and giving the option to automatically copy results to the clipboard in internet explorer.
It's free for anyone to use under an MIT licence, and everything is included in the one HTML file. You can access it directly at http://ewels.github.io/sequences/ or download and run on your own computer or server.
First written way back in 2011, revamped in 2016.