Deadlines.com is a web-based litigation calendaring program. You put in the dates of events (e.g., service of the complaint), and it will return the dates of triggered deadlines (e.g., date to respond to the complaint). You can then sync (or upload for Mac) the dates into your calendar program. It’s only $20 per case per month, a cost that can be passed through to your litigation clients.
Deadlines.com is a product of Aderant, a big legal software company serving firms big and small. This means they have an army of moles getting the latest updates to procedural rules that affect calendaring, including (in many jurisdictions) local rules. While ultimately it is every lawyer’s responsibility to calculate their own deadlines, it seems to me that Deadlines/Aderant is going to do a better job than me (or you) most of the time. There are likely other companies offering similar products.