Asparagus

Asparagus is an issue tracker with awesome 2 main Services.
At first, this issue tracker have some features like to-do-list apps. You can assign issues for today. so you can get to know what you have to do today definitely. Also, you can divide a issue to sub-issues.
Secondly, even though you are in offline, you can mange your issues in local. After that, as soon as your state becomes online, your issues can be synced with Github issues automatically!