As far as I can tell, they're positioning the tool as an alternative to something like Evite, except not exactly. You create events, which you can invite people to. Those people can RSVP yes, no, or maybe, along with a comment. You can put links to maps and other related info. So far, so Evite.
Where it's different is in the interface, a drastic change from the Evite-style interface. It's all AJAX/Comet, which is interesting, but has some pluses and minuses. It allows real-time updates and feedback from the site, but it also can occasionally get a bit laggy and sometimes fails to update properly. That's fine, I guess - it's in beta ("beeta"), so that's to be expected (to an extent).
So, this all sounds pretty good, right? Evite + AJAX == party time, right? Well, all is not right in the Renkoo world, at least not yet. Here's a list of my gripes.
1.) Events are not referenced by their name or description, but by their city and date. What do I mean? When you invite people to something - let's say Foo's birthday was coming up, and you created an event called "Foo's birthday!" and set the venue as "Foo Bar" (incidentally, if there isn't a Foo Bar in NYC, if I ever save up and open a bar, I am so naming it that) and set it for Saturday, June 3rd, people won't see the invite to "Foo's birthday!" like you might expect. They'll see an invite to "a party in New York, New York at Foo Bar, Saturday June 03, 2006". Er... ok. You can set multiple dates/times and let people vote - but in that case, the date referred to in the invite and event info will be "date and time to be determined by voting". Ooh, sexy! And so undescriptive. (Is that a word? If not, it ought to be.)
2.) As far as I can tell, no one but the organizer can invite other people or RSVP for anyone but themselves. Want to bring a date to Foo's birthday? Well, you can, but you can't indicate it (other than by leaving a comment).
3.) No auto-mapping. You need to provide your own link. WTF? They automatically grab your Flickr picture, but they can't automatically link to a Yahoo or Google map? That's just bizarre. It could be argued that by doing this it prevents them from linking to the wrong address, which happens sometimes, but why not just give an override, in that case? In fact, why not have an option where you can click to show a link to the Yahoo map, the Google map, or "insert your own url here" map?
4.) As I mentioned above, the interface often doesn't seem to refresh properly. Around 10% of the time, when clicking around, something doesn't seem to update, and the only way I've seen to fix that is to reload the entire page. D'oh.
5.) There doesn't seem to be any way to put a description of the event in there. WTF? This is a huge oversight. There is that name area, which is a large block, but it doesn't seem to be a great way to manage it. (Alternately, if you prefer, there's a very undersized box in which to enter a description, and no title/name block.)
6.) There is a "chat" area, where you see real-time updates as people RSVP and vote on time/date and so on and so forth. Very cool idea and implementation. But the problem is that the only way I can see to "chat" is by RSVP'ing - meaning you need to RSVP over and over again to have even a simple conversation in the chat room.
7.) The interface is confusing and poorly laid out. This is of course a matter of opinion, but it was the opinion of everyone I asked. It's just not intuitive, and it's not nearly responsive enough (see above) to work in its current incarnation.
8.) There are no options to ask people to bring stuff, to see what people are bringing, etc. This is a rarely-used feature on evite, but still useful sometimes.
9.) The feedback from the UI is... suboptimal. Several times you need to hit extra buttons to accomplish something that could've been simpler. Many times, it's hard to tell exactly when your changes are being saved, and what impact they'll have - for instance, if you update an event's info, will it send another email to people telling them about the change?
10.) They need more built-in event-types and icons!
11.) No way (that I found yet) to manage multiple email addresses and have them all point to the same email address. If someone invites you with both your work and home email address, you'll get two invites. Plus, they only support Yahoo chat.
12.) I forget #12.
Overall, I like the concept - there's a LOT of room to improve on Evite's implementation, but I just don't think Renkoo is it, at least not in its current incarnation. It's like... quarter-baked. And they're competing against an established competitor. (And before you ask - I already sent most of those comments in via their Feedback link. I see a lot of potential here, and I want it to get fixed up. I hate Evite.)