Jottr lets all the expenses to be added just by an email. No signup. No download. Completely Free. As and when the expenses incurs, one can simply send a email to firstname.lastname@example.org with the expense details mentioned in the subject line, eg. "samir pays 250 for entry", and its jotted. To summarize, one can send a email with subject as "report" to the same email id and the summary with the tally report is emailed to the user. As simple as that.
Do check out www.jottr.in for more details.