We use The Raiser's Edge for Donor Relationship Management (a bit like CRM except that the first word begins with D). We sent out mailings and receive donations, so that's a fairly good fit.
We have Sage for accounts. It's not to great for doing charitable type accounts, but then most charities find that and get around it with spreadsheets or third-party solutions. We use spreadsheets.
On the personnel side most of our staff are volunteers, and most don't work in this country. So personnel software isn't much use, as it thinks about employees, and payroll, and contracts and leave whereas we think about membership agreements, and seconding people overseas and strange concepts like "furlough" (the old fashioned term) aka Home Leave, and "topping up support". Personnel software doesn't care about people's children, and what medical and schooling needs they have, whereas we care about the whole family that we send abroad. So all the personnel stuff has been done in-house.
Where the people and the money come together we use the services of Wycliffe International who save us having to send money to 50 different countries, by acting as a clearinghouse. You can't get off-the-shelf software for interfacing UK accounts software with Wycliffe International, so we've done that ourselves.
We run courses, so we're like a small university with the need to book people in on courses, give them accommodation and food. We also have spare accommodation so we host conferences. We have software such as a hotel might use, but that's orientated towards individual guests, not conferences or courses. That's where my current challenges lie.