If you're a bit tired of the default Series 60 calendar then you may enjoy Enhanced Calculator, which boasts advanced features and improved usability.
Enhanced Calculator provides you with three main calculator modes: basic, scientific, and financial. As a result, you can use it to perform a range of functions, from simple addition and multiplication, to complex equations.
Using Enhanced Calculator is very straightforward and the interface is well designed and presented. I liked the way the directional pad can be used to enter the type of operation you wish to perform in the basic calculator (plus, minus, divide and multiply), and found it easy to switch calculator modes. I also found the loan calculator to be a very quick way of calculating repayments.
Perhaps the only weak point of Enhanced Calculator is that its scientific calculator doesn't include a very broad range of functions.
On the whole though, Enhanced Calculator makes for a decent replacement to the S60's on-board number cruncher.