TickTick Is a Syncing To-Do App with Flexible Scheduling Options
Web/iOS/Android/Chrome: If Astrid's pending shutdown
TickTick was built by the same folks behind GTasks, another tool we've mentioned
Adding new to-dos is as easy as typing them, and you can set deadlines and set custom reminders for specific times of day. You can set the to-do to recur every day, week, month, or year, complete with specific repeat days, so you can have a daily to-do repeat every five days, for example. You can even set when the to-do should stop recurring. Like any good to-do app, you can organize your items into lists to keep them separate, and get a daily or weekly view of everything you have coming up. You can add notes to individual to-dos, create lists with to-dos and subtasks beneath them, and share to-dos with other users.
Aside from that, there isn't too much else. The developer has "labs" features you can enable, like search, or a calendar view, but some of them are limited to TickTick's $10 or Rs. 600 per year "pro" accounts, which don't really get you that much right now, but as the service grows, it can either be a great way to try out new features or a way to nickel and dime people into upgrading. You can check out the plans here and read more about its features here.