As with any software (open source or proprietary) active development ceases after a period of time. This may be due to lack of intrest in the developers/users of that particular software or due to availability of a better software.
Same is the case with Apache also. All the projects start at incubator and based on the progress they make and intrest shown by the community will get promoted to the main. But, before using a particular software or getting involved in it's development, it's important if the development of the software is happening actively and also the bugs are getting fixed on a regular basis.
Here are a couple of ways to make sure that the project is active
- Check the mail groups if the user and the dev groups are active.
- Check when was the last, the code has been updated in SVN (1, 2).
- Check the open JIRAs and how quickly they are getting closed.
Apache has got a lot of interesting projects covering a wide area of interests and the code is open to everyone, so it's easy to get involved with Apache projects. Go ahead and get involved in one which is of interest.