BOINC is always looking for alpha testers. At the moment we only support Windows (XP, Vista, 7, 8.1 and 10) and Mac OS 10.6.0 and above. For Linux testing and support we'd like to point to your distro's package maintainer.

When you want to be an alpha tester of our software, there are a couple of requirements.
- You don't mind running potentially unstable software on your computer, which can crash at any given time and take all your tasks in cache along with it. It may be so unstable that it crashes your computer.
- You will report any unstability, any weird glitches, anything out of the ordinary to the BOINC Alpha email list. This list requires registration.
- You will keep an eye out for messages from other users on the alpha email list, to see if there is a potential big bug that needs to be checked on. Even if you cannot reproduce that bug, you will let know about it on the list.

Reporting problems can be done with screen shots (via Dropbox for instance), with an indepth description of how it does this on your system, or where applicable with a debug log, using BOINC's debug flags.
Enabling debug flags is quite easy these days, done via BOINC Manager->Advanced view->Options->Event Log options.
If for some reason you cannot run BOINC Manager, you can add flags manually to the client configuration file cc_config.xml

<cc_config>
    <log_flags>
        <task_debug>1</task_debug>
        <cpu_sched>1</cpu_sched>
        <sched_op_debug>1</sched_op_debug>
        <cpu_sched_debug>1</cpu_sched_debug>
        <work_fetch_debug>1</work_fetch_debug>
        <rr_simulation>1</rr_simulation>
    </log_flags>
    <options>
        <max_stdout_file_size>18119200</max_stdout_file_size>
    </options>
</cc_config>

The <max_stdout_file_size> will increase the stdoutdae.txt file to ~18 megabytes. Enough for you to capture at least 10 hours worth of data in.
Capture at least 15 minutes, preferably more. When sending a log in to the alpha email list, place part of your log in the post where it shows what your problem is. Please do not add a long log and just say that there's a problem in there, no other tester or developer will read that.

Do know that BOINC is being developed by the BOINC community, all of us are volunteers just like you. Reporting a problem won't always get you a reaction immediately. Have patience. Have no answer within 24 hours? Then ask again if someone else has seen this problem. Keep in mind that developers are spread across the globe, so while it may be in your morning, it can be in the middle of the night for the developer who's on your case.

If none of that is troubling you, then please let me be the first to welcome you as our new alpha tester. There is no maximum amount of testers we can use, if you have a couple of friends all willing, let them know we want them as well.

References:
Hard Bugs for more information on reporting hard bugs.
Alpha Instructions for more information about being an alpha tester.
Client Configuration Flags for more information on which flag does what?