I remember I used CacheMan on Windows XP; does it help to make Windows run better in some circumstances?
Does it work on Windows 7 too, or does ReadyBoost make it useless?
CacheMan type programs eek out a few more percentage points of performance, generally not noticeable to users. In a few edge cases it can significantly improve performance. They work by using different cache management algorithms than the operating system does, and the fancy ones (CacheMan paid-version might be one) adapt to your usage patterns better. It's a lot of effort for minimal gain. That matters to some people, though.
ReadyBoost actually does address this a bit as it adds another block-cache layer to the Windows caching system. That's one of the caches that CacheMan was managing. ReadyBoost makes things faster since it allows the block cache to be larger, so more stuff can be kept on fast media. If you've got a fast solid-state drive as your ReadyBoost device, it will offer more speedups for certain loads than CacheMan can.
For a system that is RAM constrained, ReadyBoost will offer better performance gains that CacheMan.
For a system that is not RAM constrained (you've got 8GB of RAM in a system that only runs Firefox, Outlook, and WOW) CacheMan will offer better performance improvements, but it is likely to not even be noticed.
Many of those tools were mostly placebos. They turned off unnecessary services, changed the settings for your swap file, turned off indexing, and ran a defrag on the disk.
Today, if a tool promises to optimize your PC and make Windows faster, it's most likely a virus (unless you got it from a reliable source, i.e. with a box but you probably won't because they don't really work).
Does it help to make Windows run better in some circumstances? Yes, especially if you have limited amount of RAM and open many applications at the same time, it will optimize ram usage and page file usage.
Does it work on Windows 7? Yes, I use an Intel Q8400 desktop processor in Windows 7 Ultimate 32 bits, for Website developing, but the mainboard is limited to 4GB Ram, with 3.3GB usable for the system. Without Cacheman, the available RAM, idle at 2.5GB, drops to 200MB when opening 5 browsers and Photoshop. Using CacheMan 7 on the same usage situation, the memory recovers to 900MB, and the system behaves snappier.
As for Ready Boost, using it in a Kingston 8GB Flash Card, and putting the 4GB page file on it; in combination with CacheMan did not bring any noticeable difference compared to CM alone. The literature says Ready Boost is an NT times technology, which was speed effective for 256MB to 768MB Ram systems, but above those Ram values, not a great difference was reported.
I think that it depends on the case. It might help a little on computers with very low amount of memory or with many or with plenty junk files or junk on Windows Registry. Its main purpose is your OS maintenance, but on the other hand you can’t compare RedyBoost with CacheMan, they do different things. ReadyBoost is a Windows component that lets you use any kind of portable flash mass storage system as a drive for disk cache.
I think over the years Microsoft has learned quite well how to optimize their system so the best thing you can expect is likely that the tool does no harm.
Lots of "memory optimizers" use tricks to give you the impression that they free memory while actually harming performance. Some tools for example just allocate a lot of memory for a very short time forcing the system to "give up" memory it uses to cache disk access. When looking in the task manager, the memory then appears to be free (and in fact it is free), but Windows would have freed that memory anyways when it was needed and lots of disc access is slower because it can't be cached.
Besides that, every running program uses some ressources which can't be used otherwise.