It's the biggest problem with web apps: they disappear. Desktop software is on your computer, meaning it keeps working long after the company that made it goes under or stops offering support. Web apps are totally different, as Google teaches us regularly by shutting down services people depend on.

Last year the web giant shut down Google Reader, something millions of people (your correspondent included) used every day. Just last week Google announced plans to shutter Google Code, basically ceding the entire code hosting market to GitHub.

Today we're going to look at five websites you can check to find out what Google has already shut down – and what they might shut down next.

DidGoogleShutDown.com: Crowd Sourced Speculation

Our first site attempts to predict which services Google might shut down next. It's basically a list of services and apps currently provided by the company with quick, colour-coded projections. These are followed by a few lines of explanation.

It's not an official source, sure, but crowd-sourcing means it's kept up to date. If you're wondering whether a Google service you use might go under, this is a quick place for an overview.

The site's creator seems to think Google shuts down services too quickly:

Google Wave was the e-mail killing chat hybrid app that they unveiled to a cheering crowd. It lasted 6 months, but not because the world wasn't ready for that kind of app. Slack, HipChat and FlowDock are similar apps that have long outlasted Google in that industry.

He's got a point.

Google Graveyard: Leave a Flower For Services You Miss

If you want an idea of how many well-liked services Google has already shut down, check out Slate's Google Graveyard. This site shows you a tombstone for several dead services, and lets you click to leave a flower in remembrance. There's an impressive number of flowers left for some services, including 150,000 for Google Reader alone.

I, for one, had entirely forgotten about Google Desktop before I scrolled through this virtual cemetery – let me know which services you were reminded of in the comments below.

If you need something more complete, check out Wikipedia's list of discontinued Google products.

Google Algorithm Change History: See How Search Has Changed Over Time

One Google service unlikely to shut down, of course, is search – the service is reportedly responsible for 70 per cent of Google's overall revenues. But just because search isn't likely to shut down doesn't mean it never changes, and over at Moz.com there's a great tool for looking into the history of all the changes made.

Seeing this history is essential for anyone hoping to learn about SEO, but for anyone else it's a great look into how Google thinks as a company. They add and remove search features all the time, and anyone who works online can tell you this has profound impacts on the Internet economy.

Google's App Status Dashboard: Find Out When Google Services Are Down

A service being permanently shut down is one thing, but web apps are also vulnerable to temporary outages. If a Google service isn't working, and you're wondering whether it's temporary, Google's App Status Dashboard is what you should check first.

Of course, if all of Google is offline (unlikely, but still) you might not be able to access the Dashboard itself. In that case, there are other ways to figure out if a website is down.

Google's History Page and Blog: From The Multinational Megalomaniac Horse's Mouth

Google's been around a long time, and has gotten into (and backed out of) a lot of different services. If you want a timeline of all these projects, check out Google's official timeline. This interactive page lets you scroll through the entirety of Google's launches.

That's a great place to see how Google sees its past. To see its plans for the future – including all announcements of upcoming closures – be sure to check out the official Google blog on Blogspot. Subscribe to it and you'll know exactly what Google plans to shut down next (at least, until Blogspot is shut down, at that point I'm not sure what you should check).

What Dead Google Service Do You Miss Most?

It's not like every Google service is at risk: search remains a powerhouse, and it's unlikely Gmail and YouTube will shut down any time soon. At the same time, it's understandable anyone who uses one of Google's lesser-known projects – or who is considering trying out a new Google service – might be hesitant. I know next time Google launches a new site, I'll probably watch to see how it does for a few years before transferring all my data to it.

There are plenty of dead Google projects out there, and everyone reading this can probably name at least a few that they miss. I'm wondering: which services do you wish Google would bring back? Which services are you worried might die? Let's discuss below.