Wow. The moment I get all excited about a free looper and building an Echoplex, I run into Mobius, which is a full-featured Echoplex emulation, also supporting ASIO. I will be downloading this and playing with it. The feature set, including its implementation of Multiply, looks really sweet. It doesn't include Undo yet, which is unfortunate.
Why don't I use these PC-based tools personally? For one thing, because it's a pain hooking a laptop up at a show. I like the bulletproof nature of standalone effects like the DL4. I never have to worry about CPU spikes or driver conflicts on the pedal looper. Also, I like being bound to a highly-restrictive toolkit, just for the challenge.
On the other hand, if I were starting over today--or if I decided to work in a different context, perhaps with other musicians--it would be really tempting to break out the laptop instead of my pedals.