Nothing special, I just use spreadsheets, but our income is pretty simple these days, consisting of pensions, interest, dividends and some capital gains.
For the IRS return I track the gross income from my UK pensions and interest income on a month by month basis and report calendar year totals, not those figures from P60s.
For the HMRC returns I have always just used our 1099s for my US pensions, dividends and interest with a statement that for foreign tax calculations the US calendar tax year will be considered as co-concurrent to the UK tax year. For the sale of US shares I don't sell any before April 5th each year just to keep it simple. I use the P60 figures for the UK pensions.