From the Nokia Store description:
LightWallet is a lightweight but effective user friendly solution for transaction tracking and personal finance management using your mobile phone. LightWallet supports multiple accounts, user-defined transaction categories, embedded calculator, transaction filtering, monthly reports, backup and restore using MS Excel (CSV) files and Google Docs spreadsheets.
Here's LightWallet in action:
The J2ME, menu-centric interface takes some getting used to, especially when getting started and faced with almost blank screens and no wallets, categories or transactions. However, persevere and the application soon starts to make sense. Although lightweight in concept, there's the flexibility to clear months as you go (presumably reconciling with bank statements), plus import and export facilities.
In practice, every time I've ever started to record transactions and attempt a proper wallet 'book keeping' system, I've failed - the matching up of accounting month start/end times, the transactions which overflow, the failing to input some transactions which then throws everything off.... The exercise quickly becomes a lot of work and not worth it for most people - I just scan my online or paper statements each month and mentally recognise the names of transactions of any significant amount and I'm done.
However, there are people who loves to track every expense or income, plus this could be very easily used as an expense tracker for business 'claim back' purposes. Comments welcome if you've used it in the past.
One footnote: somewhat curiously, LightWallet is listed as 'open source', despite the £1.50 price tag in the Store, and indeed the code is all online here - which means that you could theoretically take the source and build it yourself. And, being J2ME, this is presumably fairly trivial, though it's still doubtful that anyone would go to the bother, to save such a small sum. And you can't blame the developer for wanting to make a little pocket money from pre-packaging the app in the Nokia Store - it just looks a little odd to see the 'open source' presence at the same time?