There's really not any difference between a "one page business plan" and a good executive summary. The only real possible difference is the that the "one page plan" must absolutely fit on one page in a font that most people can still read, while a traditional executive summary can extend to 2 or 3 pages, but really should never be longer than that.
If you can condense your executive summary to one page, that's great. Investors don't have lots of time to read and a one-page executive summary will get the idea of your business across succinctly. It's actually a very good exercise to trim down your executive summary to the absolute minimum. This will force you to trim needless words and communicate your business idea clearly and with minimal clutter.
Whether you want to call it a "one page business plan," an executive summary, or an elevator pitch, they all should contain the following:
The content of your executive summary is by far the most important thing. Too many companies spend time focusing on presentation and graphical display of their plans when what you are saying and how you are saying it is really the most critical aspect of your executive summary. Don't get me wrong, you don't want to have an ugly presentation, but focus on the content more than anything else.
Remember, the executive summary (or one-page business plan) is usually your introductory communication with investors, so it will be your first impression. Investors will use this document to get an understanding of your communication skills as well as your ability to think critically about your business. You should spend more time on this part of your plan than any other section.
What is it? : the essential aspects of your executive summary edited down to one page.
Why would I have one? : Because once someone asked you for a one pager
Why would I need it : Because some people will only read one page to determine if they are interested.
What you would want it? Why have someone read it all if they aren't qualified or interested in joining you -- they can determine this in one page.
How do you make it? Like soup -- boil off the fat through lots of heat brought on by good third-party editors
When do you make it? When you are asked to deliver it.
What if I don't want to? How much do you want to engage the person who asked for it?
What if I can't explain the business in one page? You can. Learn the business deeper. Listen to people to the questions you are asked closer. Understand your audience better. Tell them what they are asking for instead of what you think they need.
Any ideas how to get it done? Have someone who understands business but isn't knee deep in your business interview you with the following questions:
Answer each in one simple sentence. Then convert these sentences into a document. Add a picture or a graphic and your contact information.
Then quickly mail it to the person you told you had one.
And remember that your Onepager will be the only one doc that VCs will read....