BootsnAll.com. BootsnAll.com is an independent travel Web site. They publish travelogues and travel stories, and provide trip-planning services. There are also local travel guides, maintained by individual writers, which are somewhat analogous to Wikitravel's guides. BootsnAll.com has great karma in the Internet travel community, and tends to be very positive about supporting other travel-related sites and blogs with their BootsnAll Travel Network. All content is proprietary, but it would probably be possible for BootsnAll.com to republish Wikitravel guides if they so wished.
OpenGuides. OpenGuides is a site, with custom-built software, to create city guides with Wiki software. They don't have a lot of information about the project on their site, but it seems that their mission is somewhat different from Wikitravel's. See Cooperating with OpenGuides for more details.
World66. A Wiki-based Open Content travel guide, this is probably the most similar project on the Internet to Wikitravel. It's a merger of the Capitan Cook project with the previously proprietary World66 site. The content is under the same license that we use, so content sharing is an option. Their main page says they have over 10,000 articles available, but many of their articles are at a finer level of granularity than on Wikitravel - individual attractions have articles, for example. A very interesting project.
Turismo Vikio. A Wiki-based travel guide, similar to Wikitravel, but in Esperanto. Not a lot of license or other information available, but may be an example of a sister site in another language (see Language version policy).
CouchSurfing. Great and fast growing hospitality exchange network. CouchSurfing helps you make connections worldwide. You can use the network to meet people and then go and surf other members' couches! See also Cooperating with CouchSurfing.
Travelopedia. Appears to be a German-language Wiki-based travel site.