What is Open Source? Apache versus the Free Software Foundation
The Apache license is more open than the GPL. Richard Stallman claims that version 3 of of the GPL is now compatible with the Apache license. Same Ruby points out that this is a one-way street in terms of compatibility; the GPL can use Apache code but not vice versa.
In the comments, Ruby explains:
In order to preserve the “universal-donor-ness†of the code that we produce, and in order to prevent license surprises, the Apache Software Foundation will not distribute code which has either a direct dependency on GPL licensed code, or will only meaningfully operate when GPL code is installed. None of this precludes, for example, end users from combining code from the ASF with a GPL licensed JDBC driver. Nor is this policy specific to the GPL: it applies to any license which contains more restrictive terms than the Apache License.